The Kergan brothers built a business empire serving burgers in Louisiana. The two were as tight as any two siblings could be. But that bond would be tested to the extreme when one of the Kergans disappeared.

Back in the 1980s, an astute businessman named Gary Kergan predicted the Sonic Drive-In burger chain had massive potential for growth.

"You drive up, you have the car-hop experience where the car-hop brings food out to the car and you eat in your vehicle," said Memry Tucker.

"Gary was the vision guy. I was very much more the nuts-and-bolts operator," said Gary's brother Ted Kergan.

The two men were far more than business partners. They were deeply bonded siblings.

"My story is my dad had a heart attack the day after I was born," said Ted. "Gary was in many ways like the dad that that I didn't have."

And into adulthood they remained inseparable. Ted even moved to Louisiana from Michigan to get in on the Sonic explosion with Gary.

"Gary had negotiated a development agreement with Sonic to build a lot of restaurants in the New Orleans area, and this was something that at the time was pretty unheard of," said Ted.

Gary was married to Susie, and they had a young son named Wade. Ted was single at the time. It was a tight-knit family enjoying a good life with a promising future.

Soon another partner, Larry Tucker, teamed up with the Kergan brothers.

"My dad owned Sonic Drive-Ins too, and Gary and my dad Larry were planning on buying a bunch of stores in the Baton Rouge area together," said Memry Tucker.

Since the partners lived hours from Baton Rouge, where they were doing business, they rented an apartment.

Late on the night of November 28, 1984, Gary called Ted with some incredible news.

"Gary had gone to Mississippi and had secured funding to build all these restaurants, so it was a huge deal for us, and a huge milestone in our business," said Ted.

Gary was beyond excited at what he had accomplished. He told Ted he was coming over to his house.

"He wanted to talk about it, and we kind of wanted to celebrate our success at this big milestone," said Ted. "So I said 'Yeah, this is great!'"

Strangely, Gary Kergan never showed.

"I fell asleep on the couch. I didn't realize he hadn't shown up till I woke up in the morning, and I thought it was a little odd that he hadn't at least come by and woken me up," said Ted.

If it had been anyone else, Ted may not have immediately panicked.

"Gary was absolutely 100 percent coming to my house. He never said he was coming to my house that he didn't," said Ted.

The anxiety was no more bearable for Gary's wife Susie.

"It was a significant enough event that Susie was almost hysterical. She knew something was wrong," said Ted. "I had my office call all of our restaurants to see if anybody had talked to Gary. Gary had told Larry the exact same thing, that he was on his way to my house."

"He was at the time very upset," said Memry. "He was with Gary a lot. They were very great friends. It was a shock to the system."

Ted went on a mission, canvassing every square inch of Baton Rouge.

"When I'm talking about no stone unturned, I mean I went to a store that I knew he had bought some shirts at. I mean I literally went to every single place that he possibly could have been to," said Ted. "It was literally like Gary just disappeared off the face of the Earth."

It was late when Gary was supposed to be on his way over. Ted worried he had fallen asleep at the wheel or taken a wrong turn and ended up in a dark Louisiana swamp.

Gary Kergan, along with his brother Ted and another partner, Larry Tucker, played the odds on a chain of Sonic Drive-In burger restaurants. The odds proved to be in their favor.

"At that time, they were on the verge of really making it," said author Chris Blackwood, who details the Kergan brothers' journey in her book My Brother's Keeper: A Thirty-Year Quest to Bring Two Killers to Justice.

Blackwood tells Crime Watch Daily, Gary was a respected and humble man, but one who didn't mind showing off a few of the perks of his success.

"He was driving a Cadillac Eldorado. He dressed flashy," said Blackwood. "It was the 1980s, you know, he had the gold chain and the open neck. So he did present as having money."

Did all that bling attract robbers? Kidnappers? While police investigate, Gary's brother Ted becomes a rabid citizen sleuth. Ted had plenty of access.

"Both my brother and I were fully commissioned deputies with the Acadia Parish Sheriff's Department," said Ted Kergan. "We knew the sheriff very well and had assisted in some investigations, and I probably should leave it at that."

So far the only clue was a scrap of paper with the name "Erica" written on it.

Business partner Larry Tucker found the paper in the Baton Rouge apartment he shared with Gary.

"Larry had cleaned the apartment up and thrown away the piece of paper with someone's name on it," said Ted. "Gary said 'You did me a favor, probably saved me from going out on my wife.'"

As far as anyone knew, Gary was a devoted husband and father.

"I was trying to get my arms around this concept, so to speak," said Ted.

That there could be another woman?

"Well sure, and that I didn't know who she was," said Ted.

Ted went on the hunt for "Erica." He was led to a strip joint called the Hot Spot.

"Well, I walked in and one of the dancers looked at me and said 'Hi Gary,' which was interesting 'cause Gary and I looked enough alike that that's understandable," said Ted. "I said 'No, I'm Ted, I'm Gary's brother. Have you seen him?' And she said 'Yeah, he was here last night.'"

And sure enough, Ted learned that his brother was last seen leaving with a dancer named Erica.

Police jumped on the lead, first checking out details found on Erica's license application to dance in Baton Rouge.

"Erica ultimately turned out to be Leila Mulla, who was a 19-year-old," said Ted.

"She was a former high school honor student, a violinist, a track star," said Chris Blackwood.

Ohio-born Leila Mulla came from a very wealthy family, but got herself caught up in substance abuse, and chose the life of a rebel "wild child," landing her restless soul in Louisiana, having just escaped from rehab.

Mulla worked as a stripper and a hooker. She lived in a scrappy duplex with her joltingly bizarre drifter boyfriend, Ronald Dunnagan. He was twice her age and called the shots. She was gorgeous, he wasn't. He didn't have much money and he wasn't educated. He was literally a clown on the street.

Life as a part-time street clown didn't pay the bills. Mulla's stripping and hooking did, and it turns out Gary Kergan was a regular customer.

"There was a kind of seamy relationship between the two of them," said Premila Burns, a former prosecutor with the East Baton Rouge Parish District Attorney's Office.

"Some part of me wondered if this had something to do with Gary not showing up," said Ted Kergan.

Cops high-tailed it to the duplex where Ronald Dunnagan and Leila lived. Ted insisted on coming along.

"I started to think that maybe Gary's in there and he's tied up in a closet and you know, maybe he's in some kind of distress," said Ted.

There was no Gary, it turned out. But cops made another daunting discovery.

"There was blood everywhere," said Ted. "There were parts of the walls that looked like someone had beat them with a hammer. That's when I knew for sure. Well, I knew Gary wasn't coming back."

And then they find his car.

"Yeah, I think the next day or the day after that," said Ted.

Gary's brand new Cadillac had been left in a business parking lot for five days. It was tainted with blood.

"The crime investigator said 'What you're looking at is someone died in the trunk of that car,'" said Ted.

Gary's despondent wife Susie had been clinging to hope.

"My brother and Susie were Latter-Day Saints. So they had somebody from their church there," said Ted. "We went into the house, I told them 'I just came back from the crime lab and Gary's just not coming back.'"

Even with no body to prove it, it seems inevitable that Gary Kergan had been murdered violently, and investigators have a good idea who the killers are.

Ted Kergan made it his mission to find his brother's killers. And it's a mission that would take him all across the country and into some very dangerous situations.

Leila Mulla was a gorgeous 19-year-old temptress from a wealthy family, but fate led the troubled Ohio runaway to a life of stripping and hooking on the seediest corners of Baton Rouge, Louisiana, tangled up with a street clown boyfriend pimp twice her age.

"She saw Ron as her protector," said author Chris Blackwood. "She's a very smart person so she looked for someone who could protect her and that she could kind of order around."

Leila Mulla was the last person to see missing businessman Gary Kergan, who was one of her regular clients. Blood was found in Gary's car and in the house Mulla shared with Ronald Dunnagan. Now the dubious duo is on the run.

"One of the neighbors said that they gave them some hamster cages," said Ted.

Dunnagan and Mulla got in his old car and drove to Las Vegas.

"Leila decides to go and get an escort license in Vegas, and she goes in to the sheriff's office to get this license," said Ted.

It turns out Lady Luck didn't welcome them with open arms -- instead it was cuffed wrists.

"The police in Baton Rouge had put a warrant out for a material witness for a missing person," said Ted.

Vegas cops detain Mulla. Dunnagan is hanging around the sheriff's station thinking Mulla's still working on the escort license. Vegas police have no legitimate reason to hold him.

"No one had seen Dunnagan with Gary, so there's no chance of hooking him up to the material witness," said Ted.

Turns out Dunnagan had a bench warrant for nonpayment of a traffic ticket.

"The Vegas police are very much 'I don't think we can hold a guy on a parking ticket,'" said Ted.

But Vegas cops said they would do their best while Louisiana detectives strategized.

"The police come to me and they ask me if I knew anybody in the travel business. And I said 'Yeah, we gotta get there?' They said yeah, and I said fine," said Ted.

With no time to waste, Ted hires a private Learjet.

Detectives race to the Vegas interrogation room on a mission to get Mulla to talk fast. She spills all right, pointing the finger at her drifter boyfriend Ron Dunnagan.

"She said Dunnagan killed Gary by accident," said Ted. "He said 'Did Gary deserve to die?' And she said no. The police definitely considered that a confession."

While cops search the couple's Las Vegas apartment, Ted comes along and waits in the kitchen.

"Literally I'm opening up kitchen drawers and I pull out a notebook and a diary," said Ted.

Ted's about to stumble upon some horrifying entries in that diary, which belongs to Leila Mulla.

"I get to a point in the diary close to when Gary disappeared, where she says 'Hit Gary next time. Ron will hide in the closet, that good man,'" said Ted. "My blood just went cold. I turned to the Baton Rouge detective and I said 'I think maybe you need to read this,' and they read that and they said 'We got 'em. It's premeditated, they had it planned.'"

Police bring Dunnagan and Mulla back to Baton Rouge, and the District Attorney's Office at the time is ready to pounce.

"It's circumstantial evidence, but we have plenty of circumstantial evidence. We have the people, we have the blood in the apartment, we have blood in the trunk of the car, we have a diary for God's sakes," said Ted.

But when a new district attorney named Brian Bush took over, police and prosecutors were forced to close the murder book on the case.

"Brian said 'Oh, we don't have a body, we're going to let them out.' Just like that," said Ted. "In an hour I went from 'We're absolutely going to convict them, we have them, we have the diary, we have everything we need,' to 'Oh, never mind, we're just going to let them out.'"

Former assistant prosecutor Premila Burns was assigned to the case in 1984.

"We had never tried a case without a body, at that point in time very few jurisdictions ever tried a case without a body," said Burns.

And at the time DNA testing didn't exist.

"Not only was there no body, there was blood in the back of the car that today could have been subject to DNA testing," said Burns.

But the biggest hurdle was Mulla, who was charged as an accessory. She was clever enough to know that without her, the murder charge against Dunnagan wouldn't hold up.

"The woman was refusing to testify against him and had been offered basically a walk -- immunity from prosecution were she to testify, and she absolutely refused," said Burns.

Ronald Dunnagan walked out of the Parish Jail a free man.

"It appears to me that the D.A. has placed the rights of the accused over the rights of the victims," Ted Kergan said at a press conference at the time.

"I went into a panic. It wasn't defeated, it was shock. I absolutely went into shock," said Ted.

Ted Kergan knew who killed his brother. The problem was there just wasn't enough evidence to prove it. So Ted turned private eye to bring his brother justice.

Leila Mulla and Ron Dunnagan were free for three frustrating decades.

But hope is reignited. Enter the era of DNA testing and the newly funded cold case unit of Baton Rouge Police.

"They started looking back through old file cabinets for cases they could successfully reopen and successfully prosecute," said Memry Tucker. "They start reading the words 'Sonic Gary' and they see the name 'Tucker.'"

As in Larry Tucker, Memry's father, the Kergans' friend and business partner, the one who 30 years earlier discovered that piece of paper with the name "Erica."

As fate would have it, 30 years later, Memry Tucker, now a district attorney investigator, is on the case.

"I made the 'murder book,' and we started looking for the old witnesses, everybody's name who was in any police report," said Tucker. "Step number one was to get Wade, Gary's son, to submit a DNA sample to see if the blood in the trunk actually matched Gary's blood.

"The results were that the blood in the trunk of the car belonged to Wade Kergan's father. So we knew then that it was Gary's blood, and we knew we could probably prosecute the case successfully," said Tucker.

Of course when investigators say 'Does anybody know where these two are?' you do.

"Oh yeah, I knew exactly where they were," said Ted Kergan.

Over 30 years, you hired private investigators to track them.

"Over those 30 years I did everything you could possibly think of, and probably a few things you can't," Ted tells Crime Watch Daily. "I literally knew where they were almost every day. They never made contact with each other again."

Ted discovered that Leila Mulla eventually got a nursing degree and moved to New York.

"[Ron Dunnagan] drifted back to Louisiana. He lived on a disability check, which he's told one of my people that he faked," said Ted.

The now aging Louisiana loser still pined for Leila Mulla.

"Leila was a big love of his life. She was the last person he had sex with, at 36 years old," said Chris Blackwood.

Ted recruited his close friend, a woman named Ann Edelman to buddy up to the lonely drifter. Using Ted's money, Edelman paid Dunnagan's expenses, even a cellphone. She won his trust.

Ted disguised himself as a chauffeur, driving Edleman and the clueless Dunnagan around town. The joke was on the clown.

Now, all these years later, Ted could lead cops right to Mulla's and Dunnagan's doorsteps.

"When he was rearrested, he was living at a Ramada Inn in Bossier City," said Ted.

Leila Mulla was now a nurse and a divorced mother of two living in New York City.

"I had actually gone to New York the day before the police had flown up, and scoped out her apartment building, and when they arrested her at her apartment, I was outside," said Ted.

Ted Kergan had disguised himself as a homeless man and had gone unnoticed, and watched her walk out.

"I could hear her, and she said 'I knew you would come back,'" said Ted.

Mulla is being led to a very familiar place: the interrogation room.

Detective: "This is your day to tell your side of the story."

Leila Mulla: "I know."

Detective: "Set yourself free. I think you were used, so that's gonna be up to you. You have the key to your future."

Leila knows what's coming, and from the start portrays herself as Dunnagan's psychological hostage.

Leila Mulla: "He had threatened me, threatened my family. He'd have me out on the street to try and pick people up."

Detective: "Did he take all the money?"

Leila Mulla: "He took all the money, yeah."

Dunnagan told Mulla a ghost named "Squeaky" had his eye on her.

Detective: "'Squeaky' is the ghost that could -- part of Dunnagan. 'Squeaky' was really Dunnagan. When he wasn't around, 'Squeaky' was watching you."

Leila Mulla: "'Squeaky' was a ghost, I remember that very clearly."

Even Mulla's diary entries reveal her belief in "Squeaky's" powers: "Thank God for the spirits and Squeaky, for they keep us together and keep the bond tight."

Did you buy it?

"No, but it's not only my job to see what I believe, which is very important, I have to determine what I think a jury will believe," said Dana Cummings, assistant district attorney, East Baton Rouge Parish.

And would a jury believe Leila Mulla was forced into seducing rich men like Gary Kergan?

Leila Mulla: "I met him a few times at the club. Dunnagan was always talking about, you know, getting someone for their money."

"Now Leila Mulla turns on the 'Oh, I'm so vulnerable, I'm this weak female, I was very young, I was under his spell' kind of thing," said Cummings.

Detective: "See on this journal entry, you have 'a plan to get him next time. Ron hid in the closet, that good man.' You said, let's see, 'I had $240 from Sonic Gary.'"

Leila Mulla: "OK. I don't remember how much money."

Detective: "Do you remember writing that?"

Leila Mulla: "No."

Detective: "What do you think you were referring to there?"

Leila Mulla: "I don't know."

Interrogators have had enough of the cat and mouse game.

Detective: "I think you are lying. You have selective memory, you're gonna talk to me? You've been dragging this on."

Leila Mulla: "I'm going to tell you what happened."

Detective: "OK then start telling me, lets quit the dance."

Mulla slowly lays out the cold-hearted plan. Note the journal entry that reads "let go of animals."

Detective: "He bought some type of poison and was poisoning animals."

Ron Dunnagan experimented on guinea pigs and mice.

Leila Mulla: "I think that it was a powder."

Mulla's role was to lure Gary Keran to their home and serve him a deadly concoction.

Leila Mulla: "It's true about the wine, it was tainted. Dunnagan was hiding in the closet. Gary started to [choking sound], and Dunnagan drug him out of the room."

According to Mulla, Dunnagan took Gary into the bathroom and performed the unthinkable.

Detective: "You have to tell us, Leila."

Leila Mulla: "I know I do. I know, I know. I know. He cut him in half, OK. He cut him in half. I know it was a saw."

Detective: "A handheld saw or motorized saw?"

Leila Mulla: "No, it was a little saw."

If Mulla's story is to be believed, Gary's remains were stuffed in trash bags, thrown in the trunk of his own car and driven by Dunnagan and Mulla to dumpsters along a highway.

Leila Mulla: "It was foresty, it was a green dumpster. I remember there were lights though, so I know it wasn't a rural area."

Mulla says they took a cab back to Baton Rouge, and then Dunnagan wiped the apartment clean. Cops are dubious.

Detective: "Let me tell you something, when a body gets cut in half, the guts come out and blood goes everywhere."

Leila Mulla: "But I did not see any blood."

For all its peculiarities, Mulla's story was strong enough for prosecutors to move forward even without a body. Once again, Mulla was offered a plea deal in exchange for her testimony.

Could you have convicted Ron Dunnagan without Leila Mulla testifying?

"We didn't have enough evidence to indict him without flipping her on him," said Dana Cummings.

This time Mulla accepted a plea deal that no one would call sweet: 30 years in prison.

Because of Leila Mulla's testimony Ron Dunnagan got life behind bars.

Perhaps the sickest part of this crime was the motive. If you thought it was money, you were wrong.

"They wanted to kill someone, according to Leila, just to see what it was like," said Ted Kergan. "A 'thrill-kill.'"

"I'm just so grateful that Ted was able to push the case, keep the case alive -- because he did, he kept the case alive -- and was able to see justice served. That's huge," said Dana Cummings.

Ted Kergan is satisfied as well. He just expresses it in a less delicate way: "At the end I said 'After 30 years, I got you, you son of a bitch.'"

And this story isn't over for Ted. He promises to never give up until he finds his brother's body, no matter how long that takes.