This month hundreds of thousands of students will finally graduate from college. Donald Dunn's parents had been anxiously been waiting for that day. But on the day they were to celebrate with their son, things took a tragic turn.

A woman makes a chilling 911 call on May 25, 2013. Police respond and find a gruesome crime scene. But is there more to this murder than meets the eye?

It appears to be another tragic case of domestic violence. But these cops are about to uncover the most sinister, cold-blooded murder plot they've ever investigated.

Mark McDermott was a successful businessman, an Australian who found love and a new home in rural West Virginia. Mark married Johanna, who had a young son named Donald Dunn.

According to Mark's sister Tracy, who we reached via Skype in Australia, Mark McDermott treated Donald like he was his own.

According to Donald's close friend Alex Wills, when Mark and Johanna separated for a short time, Donald insisted on living with his stepfather, not his mother. Mark even paid for Donald's education at Marshall University, where his stepson lived with his fiancée.

"Donald led a very comfy lifestyle. He never wanted for much," said Wills. "He went on trips to other countries with his stepdad. His stepdad always gave him what he needed or what he wanted, including a nice car, nice clothes, a roof over his head, just a very comfortable lifestyle."

Was Johanna somehow jealous of this relationship? When she was suddenly stricken with cancer, she waged the battle with Mark's love and support. So why would she snuff him out with such malice?

On the day Mark was killed, the family was preparing for a celebration: Donald was graduating from college.

According to police reports, Mark was in the living room reading on the couch. Donald was downstairs getting ready for his big day.

"He was taking a shower, getting ready for graduation and while he was in the bath apparently he claimed that his mother shot his father he came out, saw what had happened and was aghast that something had happened to his father," said Raleigh County Sheriff's Captain James Bare.

Raleigh County Sheriff's Sergeant Greg Kade was one of the first to arrive on scene.

"When we first got into the residence we observed a female, she appeared to be in a state of shock, and then we come upon the living room and we observed a white male, middle-aged, slumped over on the couch with an apparent gunshot wound to the head," said Kade.

Two gunshots, both through the skull. It appears Mark was reading a book when he was killed, caught completely off guard. Police find the murder weapon on the dining room table.

They also discover a suicide note, apparently written by Johanna to Donald, in which she states she couldn't stay "trapped in a loveless marriage" any longer, and apologizes that she won't be there to "see the man you become."

Officers take Johanna into custody, and Donald is brought back to the Raleigh County Sheriff's Office to get his statement.

That's when things take a wild turn.

It was supposed to be graduation day for college student Donald Dunn. But police say the only thing this 23-year-old would be graduating was from amateur liar to professional killer.

Mark McDermott, 54, was shot dead, at the hands of his wife Johanna by her own admission.

Captain James Bare is called in to question Johanna and Donald. Both are placed in separate interrogation rooms.

"He initially told me he conveyed the same story to me that he had to everyone else, basically that he was taking a shower and his mother shot his father," said Capt. Bare.

But when he speaks with Johanna, she drops a bombshell.

"At some point she switched from 'I shot him' to Donald had shot him," said Capt. Bare.

Capt. Bare also notices something odd about Donald.

"He was just plain as could be, he never was emotional, he was never upset, he never was angry, he was just pretty much flat the entire time," said Capt. Bare.

Capt. Bare hammers Donald with Johanna's story.

"He was surprisingly easy to break as far as the confession goes, because I confronted him with what I knew and what my suspicions were, and he pretty much just broke at that," said Bare.

Donald confesses to killing his stepfather -- but the how and why is almost unbelievable.

It turns out, Donald had flunked out of college years earlier, although he continued to produce phony report cards and to tell everyone -- including his fiancée -- that he was still a student.

"He had been living a lie for about two years pretending to be a college student," said Raleigh County Sheriff's Detective Cory Suman.

So on the day of his graduation, Donald knew he was about to be exposed.

"He said that he had been planning this at least since spring break. He knew that eventually he was gonna have to graduate so he had known for a couple months that he was gonna have to do this," said Capt. Bare.

"He was going to the gun range and he was target-practicing with multiple friends trying to learn more about guns, which he was never really into in high school," said Alex Wills.

"He had taken that gun from his mother's drawer, it was his mother's gun, and had had it with him during the time he was home preparing for graduation," said Capt. Bare.

"It's just senseless to kill someone to cover up for a lie -- to me it's just incredibly selfish," said Det. Cory Suman.

But it gets even crazier.

"It was supposed to be a murder-suicide," said Det. Suman.

But it wasn't a typical murder-suicide -- far from it. When Johanna came home from running an errand that day, Donald had already shot Mark twice in the head. But his plan was only half-complete.

"When she came in he said 'Mom, I have something for you,'" said Det. Suman. "She thought it was a present or something, and for him graduating, so he sat her down on the bench and that's where he said 'I want you to close your eyes, I've got something for you,' and that's when he took the gun, pressed it up against her head and pulled the trigger.

"She heard a 'click,' she opened her eyes, realized there's a gun," said Suman. "The gun actually failed to function because when a semiautomatic, if you push the slide enough out of battery, it won't function properly, which is what saved her life."

Shocked, his mother manages to knock the gun away.

According to Johanna's testimony to police: "He said 'Just hold still and it will be over with.'"

And Johanna's suicide note? Donald had typed it out to justify a murder-suicide by his mother against Mark.

"His reasoning behind all this was that he thought it'd be easier to just kill his parents as oppose to tell them the truth because he didn't want to disappoint them," said Capt. Bare.

Acting quickly, Johanna convinced Donald that she could take the rap for the murder, stating: "I said 'How about if I say I shot him?'" He finally agreed, which led to the 911 call.

During her interrogation, Johanna said: "One of us needs to be locked up, because he will try to kill me again."

"I was in complete shock 'cause you know being that close to him throughout the years I just, I never saw that coming," said Alex Wills.

"He had just no emotion, no care, just, it was all about him and only him and he could care less about anything else," said Capt. Bare. "He even had a game plan for how he was gonna react and his plan for the future after, if he was able to pull this off. His game plan was he was gonna ride the swell of emotion that he got and the sympathy that he got from people to try to get him through financially or whatever he could get, for quite some time, then he planned on 'getting fit' as he put it, and he said he planned on going into law enforcement, actually."

In fact, during his confession, Donald told police that after he shot Mark, he "expected to be physically ill or you know at least worried, it's not there."

Mark McDermott's family in Australia is understandably devastated.

"Still to this day I'll never make sense of it because it's just a heartless monster that was born and took my brother. Lost his life for showing too much love," said Mark's sister Tracy McDermott.

"I think he's in the right place," said Bruce McDermott, Mark's father. "And he's going to be there for the rest of his life. Not going to bring Mark back, but."

Donald has never expressed remorse for his actions, and even told Captain Bare he would do it all again.

"I asked him, 'Why didn't you just come clean with your parents and tell them the truth about it?'" said Bare. "He just completely said that he thought it would be easier just to kill them, as opposed to telling them the truth."

Donald Dunn was sentenced to life in prison with no chance of parole. Surprising to many, his mother Johanna -- who declined our interview -- continues to maintain a relationship with her son, even though he was one click away from taking her life.

Dunn appealed his conviction and sentence all the way up to the West Virginia Supreme Court of Appeals, but the high court upheld the decisions. He will now spend the rest of his life behind bars.