Mark Waugh, 23, was knifed to death inside the tiny apartment of his friends Rahul Gupta and Taylor Gould in October 2013.

Mark died a slow, agonizing death. But who would inflict such violence and venom upon the young law student? Which of these upwardly mobile intellectuals savagely plunged a kitchen knife into the body of one of their closest friends?

For even the most seasoned detectives, the answer won't be easy.

George Washington University biomedical engineering graduate student Rahul Gupta shared a tiny studio apartment on the 16th floor of an upscale high-rise building with girlfriend Taylor Gould, a physics researcher for the U.S. Food and Drug Administration.

The young couple and Rahul's good friend, Georgetown law student Mark Waugh, are out on the town in Washington, D.C.'s trendy Dupont Circle.

"It started as a happy occasion. It was a birthday celebration for Rahul Gupta," said Bethesda Magazine Digital Editor Andrew Metcalf.

Another friend, Josh White, joins the group at a local bar to celebrate the occasion. It's a night of hearty laughs and heavy liquid consumption. Rahul's topped off the booze with some earlier hits from the bong.

"There's a lot of drinking going on by all the parties involved," said John McCarthy, state attorney, Montgomery County, Maryland. "It was considerable, especially in Ms. Gould's case."

Just before 2 a.m., Josh White heads home. Security video shows Mark, Rahul and Taylor returning to the couple's Silver Spring, Md. apartment.

"You see them come in together. They're like any three young people that have been out," McCarthy tells Crime Watch Daily. "They've been at the bars and they're acting a little intoxicated. But there doesn't appear to be the kind of tension that's going to erupt."

But something goes terribly wrong once they're inside the apartment.

Taylor Gould makes a call to 911. One could hardly call it frantic.

911: "Do you need police, fire or medical?"

Taylor: "Um. Police."

In fact, Taylor is disturbingly vague.

Taylor: "Um, my friend is uh, I just, he's here and I need emergency right now."

911: "What is going on that you need the police, what is happening?"

Taylor: "I don't know."

911: "Taylor, why did you call 911? What's going on?"

Taylor: "Nothing."

911: "You're not answering my questions so I need to talk to somebody who will."

Taylor: "What do you want me to answer for?"

911: "I need to know why you called so I can make sure I'm sending the correct help."

"There would be long pauses on the 911 where she just wouldn't answer at all, or she would just give the same answer over and over again," Montgomery County Police Detective Paula Hamill tells Crime Watch Daily.

911: "The way that you've been answering questions, something's not right. You need to tell me."

Taylor: "I'm sorry."

911: "What is happening?"

Taylor: "I need someone here, there's blood everywhere."

911: "What do you mean there's blood everywhere? What happened?"

Taylor: "I don't know."

911: "Who is bleeding?"

Taylor: "I don't know, I just want someone here."

"It was very disturbing. It was nine to 10 minutes long," said Jennifer Page, Rahul Gupta's defense attorney. "I think that was as long as anything that happened in the apartment, was her 911 call."

Even more perplexing, the dispatcher can hear an angry voice in the background.

Voice: "Where the f--- is the f---ing police?"

Taylor: "I don't know."

911: "Taylor, hello, could someone come back to the phone please."

Voice: "Shut up. Please!"

Voice: "Get the f--- off of me, don't touch me!"

Taylor: "I didn't do anything wrong."

Voice: "[sobbing] No. I didn't do anything wrong OK, stop, f---ing a------."

Taylor: "Yeah. I'm here."

911: "OK. I need you to talk to me, because I don't know what's going on and all I hear is people saying to get off of me."

"You hear Taylor giving very bizarre, unresponsive answers," said defense attorney Jennifer Page. "She puts the phone down several times. She moves away from the phone."

Having no idea what to expect, police race to the apartment and discover a scene of pure chaos.

"There was blood all over the apartment. They had Ms. Gould answer the door with blood on her," said Detective Paula Hamill. "They observed Mr. Gupta lying next to Mr. Waugh and then they quickly realized that Mr. Gupta was still alive."

But Mark Waugh suffered a different fate, lying in a bloody pool, his body riddled with stab wounds.

"We are talking about a person who is bathed in blood. There were defensive wounds, there were jugular injuries," said John McCarthy. "He died savagely."

Taylor Gould's body was blood-stained. Her mind was distressed. Taylor's boyfriend Rahul Gupta is just plain aggravated.

Rahul: "I want to get out of here. I want to s---, I want to poop, I want to eat. I'm hungry."

They're each being interrogated at the Montgomery County Police Department in Maryland.

Rahul's high school buddy, Mark Waugh, an Eagle Scout, champion debater and Georgetown University law student, is dead, savagely knifed to death in the studio apartment of Rahul Gupta and Taylor Gould in Silver Spring, Md.

"There were 11 stab wounds," said Jennifer Page, Gupta's defense attorney. "There were five or six that were the important or fatal wounds. The other five or six were characterized as defensive wounds."

A night of heavy partying and utter inebriation turned deadly inside the 500-square-foot efficiency apartment.

"The murder occurred in a very, very small room," said state attorney John McCarthy. "When the individuals were in this apartment they would have been in relatively close proximity."

But somehow neither Rahul nor Taylor knew what happened -- or so they say during the police interrogation.

Hamill: "Is there even a remote possibility that you did this to Mark and you don't remember?"

Taylor: "I can't imagine hurting someone like that."

Rahul: "If I wanted to stab Mark I would've remembered every detail of it."

Veteran homicide detective Paula Hamill knows how to play the mental chess game that comes with interrogating witnesses -- even when those witnesses are brilliant scholars.

Hamill: "At what point did you two well-educated people say 'What the f--- happened,' like, 'Why is this dude dead in my apartment? Like how did he get hurt, or what's wrong with him?'"

Taylor: "I don't know."

Hamill: "Did you ask her? 'What the f--- happened?' Like, any normal person would be like, 'What the f--- happened?' So you didn't ask?

Rahul: "Probably should have done that, yeah."

Were they truly memory-impaired? Blackout drunk? Covering for each other? Lying? Or some sort of twisted combination? Detective Hamill hadn't yet pinned it down.

"I really had a difficult time with her and with Mr. Gupta because I feel like they were both so deceitful throughout the entire interview process that it made it very frustrating to try to grasp on to any little bit of truth," said Det. Hamill.

Detectives are going in circles trying to figure out who killed Mark Waugh. They decide to try something unique: They put both of them into the interrogation room to see what could be revealed.

"We wanted to see if it caused any type of spontaneous statement or utterance from either one of them with regards to what really might have happened inside the apartment," said Hamill.

Rahul: "I didn't do s--- to Mark. I did not stab him."

Taylor: "I don't think I did either."

Rahul: "What happened?"

Taylor: "I don't know, I'm freaking out, OK? I don't know."

Rahul: "Did you stab him?"

Taylor: "I don't think so. I don't know what happened."

Rahul: "Go out there and tell them that I want my lawyer. If I don't get a lawyer then I'm going to sue. Go out there and tell them that."

Taylor: "Can I kiss you, or no?"

Rahul: "Not right now."

"We didn't learn anything," said Det. Hamill. "I don't think we were any further ahead when we finished having them together than before we put them together."

It's back to square one. But in time, Det. Hamill notices cracks in the armor.

Hamill: "When is the last time that you and Tay' had consensual sex?"

Rahul: "Um, yesterday."

Hamill: "Like before you went out, or?"

Rahul: "Wait, hang on. What day is it today?"

Hamill: "Well, it's Sunday now."

Rahul: "It's Sunday, OK. So we didn't have sex yesterday. So it was Friday then."

Detective Hamill asks Rahul that question for a reason. She's discovered that lovebirds Rahul and Taylor hadn't exactly been cooing over each other in recent months.

"There was a lot of tension. There was some information we later gathered about the fact that Mr. Gupta and her relationship was not a completely satisfying relationship on a sexual level," said John McCarthy.

Investigators wonder if that unhappy relationship may have played a part in Mark Waugh's murder.

"The issues stemmed mostly from her flirtatiousness with other men and I believe their drinking," said Hamill.

"A couple of Rahul's friends had had experiences where they believed that Rahul's girlfriend Taylor had been hitting on them, flirting with them, to the degree they were uncomfortable," said Jennifer Page.

Remember Rahul's bar-hopping birthday gathering in Dupont Circle the night before? And the other friend, Josh White, who had joined the group for a while? Listen to what White told detectives about Taylor.

"She has a tendency to be a little flirtatious to Rahul's friends. And I just asked her like straight up, like 'What's the deal, like, you're a little flirtatious,'" Josh White says.

In fact Josh says he felt Taylor was shooting some flirty vibes his way that night. He says he felt uncomfortable and unsure what to do.

"Nobody wants to say 'Hey, the girlfriend you're apparently very close with is hitting on your friends,'" said Jennifer Page.

But Taylor insists it was Josh who was making the moves on her, so she turned to Mark for advice.

Taylor: "Josh was texting me and it was really weird and he was kind of hitting on me. So I told Mark, because I was kind of like, What do I do? This is Rahul's friend, I don't know what to do, so."

Taylor claims she was so uncomfortable with Josh's alleged advances and the tension brewing with Rahul, she just wanted to go home.

"There's some confusion about exactly who was flirting with who, and this resulted in a disagreement," said Andrew Metcalf, Bethesda Magazine.

Was that a pivotal point in the evening and that's why they all decided to part ways?

"I do think that it broke the evening up," said Jennifer Page.

Josh splits from the group. Taylor and Rahul leave the bar and head home with Mark tagging along. Taylor tells police Mark wanted to comfort and advise her about the flirtation issue.

Taylor: "He wanted to like talk me through the whole Josh thing, because I was really freaking out."

But some find it curious that Mark would come back to the couple's apartment just to counsel Taylor about Josh.

"First of all, if there had been an issue with Josh, he was now removed from the situation and certainly there were a lot of opportunities for people to talk about this later," said Page.

So why was Mark Waugh there, and how did he end up dead?

"A young man who was a good friend of yours died a violent death inside your very small efficiency apartment. I find it very hard to believe that you didn't hear it, see it, and know what happened," said Det. Paula Hamill.

Rahul Gupta claims he didn't murder his friend Mark Waugh, so it must have been his girlfriend Taylor Gould. She, on the other hand, says she blacked out and can't remember a thing.

They're attractive, brilliant, successful 20-somethings But could they possibly be millennial murderers?

When Taylor accused another friend, Josh White, of hitting on her at the bar, causing tension with Rahul. According to police, Taylor told Rahul she wanted to go home and she wanted Mark to come with them.

"Taylor wanted to bring Mark back to the apartment because she believed he could advocate on her behalf to Rahul that she wasn't flirting with this other guy who was with them," said Andrew Metcalf, Bethesda Magazine.

Security cameras capture the three returning to the couple's apartment

"In the elevator Mark is kind of making funny faces and nobody appears to be angry. Nobody appears to be fighting," said Jennifer Page, Rahul Gupta's defense attorney.

But behind closed doors, a disturbing drama is unfolding. Taylor calls 911, but it's a mysterious exchange, full of critical omissions.

911: "Why did you call 911?

Taylor: "Rahul, are you OK? Stop."

911: "Taylor."

Taylor: "I'm trying to understand what's going on."

There's clearly another voice yelling in the background: it's Rahul Gupta. Still, Taylor tries to convince the dispatcher she's by herself.

911: "Who else is in the house with you right now?"

Taylor: "It's just me."

911: "No, there's males in the house too. Who are they?"

Taylor: "My friend, hold on."

Rahul: "Get the f--- off of me. Don't touch me."

"So obviously her and Mr. Gupta were having some kind of an argument," said Detective Paula Hamill.

When police arrive, Mark Waugh is dead. At first the couple puts up a united front of ignorance.

Rahul: "At some point I woke up and I realized, well OK, this guy is bleeding out."

Hamill, to Taylor: "Mark is dead."

Taylor: "What? Oh my God. Oh my God. What happened?"

Hamill: "So, that's what we're trying to find out."

Taylor: "But how did he die?"

Hamill: "I don't know."

What clues cops can't get from Rahul and Taylor, they find from the grave. Mark's cellphone reveals troubling tension in the apartment. Before he's killed, he texts a friend:

2:01 a.m.: "My night is becoming historically akward." [sic]

2:19 a.m.: "Im about to gnaw my hand off so I can leave in the ambulance."

Finally, at 2:55 a.m.: "Awake? I need help"

Mark was in the bathroom at the time, according to police.

"He made a statement about being in an awkward situation," said Det. Hamill. "That makes me wonder if maybe Ms. Gould was making some type of advances on him. "

Hamill: "Were you in bed with Mark at all during the night?"

Taylor: "Absolutely not. No."

Hamill: "Did you have sex with Mark? Anything happen with Mark during last night?"

Taylor: "No."

Detective Hamill pushes a little harder, but now she's armed with an interesting police photograph.

Hamill: "When police got to your house, you weren't wearing this, because they have pictures of you. You had like a white T-shirt on and pink underwear.

Taylor: "I'm kind of surprised I wore that in front of Mark."

Police discover another outfit: Taylor's red dress and bra that she wore out that night.

Hamill: "They found that red dress there. But it's got bloodstains all over it. You just can't explain that?"

Taylor: "I -- no. I'm -- Like clearly I, you know, interacted with the body because I had blood on me. I just don't know when it happened."

Police discover strands of hair on the murder weapon, in Mark's hand, and stuck to the bloody wall.

"It's my understanding it was a long blonde hair, and the only person that had long blonde hair was Taylor," said state attorney John McCarthy.

And another curious discovery under Mark's body:

"When he was rolled over, still stuck to the back of his jeans, on that little square of leather, was a perfectly stuck unharmed soft contact lens that was Taylor's prescription," said Jennifer Page.

Still charged with nothing, Taylor's recollection of events, or lack thereof, wave serious red flags.

"The flirtation, the unanswered questions about her hair and her contact lens, her bizarre behavior on the 911 call and the fact that she changed clothes," said Page. "She had a pair of shoes and she had her car keys on top of the blood and all of the pictures taken by the police support that these items had to have been put after the bloodletting.

"It appears she was trying to leave the apartment," said Page. "For what purpose I can't hazard a guess."

At this point there's only one thing Detective Hamill believes for certain.

"I believe that she knows everything. I believe that she knows what happened, and I believe that she knows why it happened, and I believe that she saw it happen, and why she chose not to tell us, I can't explain," said Hamill.

Rahul: "I don't want to be here anymore."

Rahul Gupta is trapped in a police interrogation room.

Rahul: "I want to see my lawyer."

Hamill: "And I explained to you that we don't keep lawyers here at the police station."

Rahul: "But you can't just keep me here then."

Hamill: "I can keep you here. Yes I can, in the holding cell."

Rahul: "When do I get to go? Like when do I get to sleep in a bed or take a s--- or eat?"

"Here he's being told by detectives that your friend from childhood is dead," said Patrick Mays, assistant state's attorney, Montgomery County, Maryland. "Mr. Gupta expresses no sadness at all. His response is he's tired. He's hungry. He wants to go home, he wants to take a shower."

Hamill: "Is it possible that you did it, if you don't remember? You've said you know for a fact that you didn't do it, but you really don't know for a fact that you didn't if you don't remember what happened."

Rahul: "I know for a fact I didn't do it."

Rahul Gupta and his girlfriend Taylor Gould were the only other people in their postage-stamp-size apartment when Mark Waugh was stabbed to death with a kitchen knife. Rahul's live-in girlfriend Taylor insists her alcohol-saturated memory has failed her.

"She didn't really definitively say she didn't do it," said John McCarthy.

Rahul: "Did you stab Mark or no?"

Taylor: "I don't think, like -- I wouldn't do that. Why would I attack someone?"

"She in fact said that she didn't know what had happened, that she was blacking out during the incident, and she even said that she didn't want Gupta to be accused if she had done it, or if there was evidence that she had done it," said Andrew Metcalf, Bethesda Magazine.

Taylor's booze-induced memory loss was her boyfriend's gain. Rahul seized the opportunity to weave a story rich with veiled accusations, with his girlfriend the intended target.

Rahul: "I didn't stab anyone but as soon as I found out that Mark had been sort of punctured here I tried to stop the bleeding. I tried to give him CPR. I kept telling Tay' to call the police and she sort of -- I don't want to say hesitated, but just sort of looked at us."

"He is explaining, he is minimizing, he is shifting blame, and he's very intelligent, so I wasn't surprised he made that decision," said Patrick Mays.

Then Rahul becomes even bolder with his version of events.

Rahul: "I'm going to be honest with you. Something happened between Tay' and Mark, and then Mark was bleeding out. So I came to his medical attention, I tried to stop the bleeding."

It appears Taylor is being thrown under the proverbial bus.

Rahul: "When we all three of us got back to the apartment it was clear that something was going on."

Hamill: "OK, like clear because, did you see them kissing or touching? Just the way they acted?"

Rahul: "No, yeah, the body language, and I sort of just looked the other way. I sat down and just started doing my own thing. And at some point Mark sustains injuries."

Then Rahul goes in for the kill.

Hamill: "If you didn't stab him, then who did? Tay?"

Rahul: "Yeah."

It was a stunning accusation, Rahul Gupta ratting out his own girlfriend, putting the knife in her hand.

Hamill: "He says he didn't do anything to him, therefore you must have done it."

Taylor: "Oh my God, oh my God."

Hamill: "Rahul says that he felt like something was going on with you guys."

Taylor: "What?"

Hamill: "You screamed, started screaming and that he turned around and that Mark was on the ground bleeding. I mean, what reason would you have to hurt Mark? You didn't wake up to like him trying to f--- you?"

Taylor: "I don't remember anything."

What are cops to do? They've got Taylor's blank memory, Rahul's adamant denials -- they're both in an alcohol fog and there's no proof that either is lying. Blood and hair evidence is useless because both Taylor and Rahul live in the apartment.

Investigators comb through every detail of the case, and become intrigued by one of the 11 stab wounds.

"This was a stab wound from the back that went seven inches into the body of Mr. Waugh," said John McCarthy. "It actually chipped a bone as it entered his body."

It was strike one for Rahul.

"Ms. Gould, at five foot, 100 pounds, would be physically incapable of having been the person delivering the blow," said McCarthy.

Then, a critical revelation: Investigators believed Gupta had the psychological wiring that could lead to murder.

"I know an ex-girlfriend that said that he became a different person when he was drinking, and I know that that girlfriend had roommates who wouldn't allow him to their shared house any longer because they didn't feel safe," said Detective Paula Hamill.

A motive for Mark's murder seemed now seemed easy for cops to nail.

"Jealousy. Jealousy," said John McCarthy.

Then came a bombshell in a recorded jailhouse conversation between Rahul and his father.

Dad: "What happened?"

Rahul: "Mark and I got into a fight and he tried to get a knife and then I -- "

Dad: "Who?"

Rahul: " -- got the knife."

The phone call is a golden nugget for police and prosecutors. Rahul admits to a fight with Mark, and he appears to say he "got the knife."

During police interrogation, Rahul had said: "I found out that Taylor and Mark may have been going out or something behind my back."

Rahul Gupta is charged with murder, and during trial -- not open to cameras -- he continued with his fantastic explanations.

"The story that he gave was so unbelievable," said prosecutor Patrick Mays. "I mean it was just absolutely incredible. That he had bumped his head. He had fallen down and that somehow during the time that he was laying on the floor, an unprompted murder was committed by his inebriated girlfriend."

While Rahul continues to blame Taylor, she testifies for two days and does not back down from her claims of memory impairment -- but Taylor never blames Rahul.

Then the jury hears what is potentially a nail in the coffin for Rahul. According to court documents Rahul told cops when they arrived at the scene of the murder: "I walked in on them cheating and I killed my buddy."

"I think that that was probably the most honest statement that he made that entire night," said Det. Hamill.

But Rahul quickly recanted his confession after sobering up, claiming he was only trying to take the fall for his girlfriend.

"The wheels in his head are turning and he's coming up with a way to try and get out from under the criminal liability that he knows is coming," said Mays.

But even the handsome young intellect couldn't outsmart the jury. It took less than five hours to convict Rahul Gupta of first-degree murder. He was sentenced to life in prison.

Rahul's defense argues the jury's decision is unwarranted.

"I believe that the evidence in the apartment about her behavior that night should have made the jury find regardless of what they found her involvement to be, there were just too many questions about what Rahul's involvement was, and he should have been found not guilty," said Jennifer Page, Rahul's defense attorney.

Rahul Gupta has exhausted all state appeals. His life sentence stands.

Taylor has never been charged. Crime Watch Daily tracked down the woman at the center of a tragic murder, hoping to hear her story in her own words, but she declined to speak.

"The fact that she wasn't charged with anything doesn't mean that I personally don't believe that she has some culpability in what happened," said Det. Paula Hamill. "I just believe that her culpability doesn't rise to a level of a criminal nature. But I think it is a hard memory for her to live with for the rest of her life."