A look at the shocking investigation that put a serial killer behind bars

The two-state investigation, which spans a love triangle, at least two murders and allegations of cannibalism, is the focus of Investigation Discovery's two-part series, "Dead North."
8:55 | 07/06/18

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Transcript for A look at the shocking investigation that put a serial killer behind bars
pact. Here's ABC's linsey Davis. What would the biggest piece of B bet you -- I mean -- torso. Torso? Eporter: Kellycchran, in handcuffs, is leading iron county pe chiefizzo to a breakthrough, all caught body cam. 'S saying everything is here, the skull -- order: A man named Christopher Regan has been missing for 1 monthnd Kelly is thenly person alive who ma know what happened. Dog's india. That's what it does Yep. Without indicate as to where Kelly H just shown me, the dog went directly T that tree and indicated the scent and the sour of human remains. Reporter: For nearly T years, chief riz doggedly pursued this case that made headli brut murders. Allegations of cannibalism. And a cat and mouse justice across several states. This became your lif it did. It cond you? It DI Oh my Reporter: Chief Rizzo's hunt for the truth I showcased in a two-part investigation disry series D north" whichveshours of real police bod and tear deviation foo with glossy re-enact manies. It's not a missing per case, this is a murder. Reporter: It Michigan's upper peula, October 2014, Christopher Regan is recorded missing from iron county. Chief Rizzo is on thee and learnsan has been sleeping with a married woman named kel cochran.she questions Kelly and husband Jason a sees red flight away. What's your initial react when you meet th Watching and listening to the interviews, you know,at T I knew that T was -- something wasn't right, there was most defely a possibility of their invoent. Hi, I'm C Rizzo with iron county police, nice to mee U -- Reporter: Chiefizzo wonders if jealousy ove the affair may have something to do with the missing N. She eventually ga search warrant to enter the Cochran ho police gatherevid. But make no arrests. Then, R theloak of darknethe cochrans flee to Indiana. Male pack their thinnd take them, they don't just leave everything behind. Which ishat they did. Reporter: The neighbors they left beh in Michigan tell ch Rizzo cochrans began behavingtrangely around the tihrisan went missing using power tools in the middle of theht. Then came an invitation for Dinn Kelly Jason asked if want to come overor dinner one night. I was like yeah, sure. Th two day after Chris missing. Ll of a sudden, in week, they're havingm over to their H for Dr. And they've got all this meat. W'd they get that meat, where'hey get the money for it? It was definitely song I never ate before. It was like a transparent of like meat. Like a lobster or shri How mucore disturbing did mak this whole rio? That was the F time I was ever brougo think that they could dismemberedhim. I just sat backny chair listening and thinking, T can't be Repr:le Michigan oritiesuggle to make headway ihr Regan's disappearance across state lines in Diana, authorities receive a phone call that sparks R own investigation. L county 911. Reporter:ain, Kelly Cochran is at the cr fit. She calls 911 about husband, Jaso His face isike blue, he's breag rely, I don't know 'S wrong. Orter: Jason Cochran up dying. Iept thinking that some was going T en. Either he's going kilr and killhimself, O -- I J kept ting someone's going to end up dead. And it happened. Eporter: Theopsy report rules son's dth ahomicide. Toxicology showed aarge amount of heroin in his body. Bu he had been scated befon dose could kill him. Nowt signs point toward Y being involved in her husban death, hobartndiana detective Jeremy ogd sees an opportunity to get Kelly talkin You help with things to do withat witness, not suspect. Reporter: He H this case will lead to ans about WHA happened to Chris Regan too. I wanted all the pie of theuzzleo come together. I knew theinning that the only wayoolve both of the murders was to get hero admit what happened tohris Regan and die the location of Chris Rega Rter: Detective Ogden comes up with plan to spook lly using a close friend of Jason's namedalt Ammerman calling with red herring, preten her husband Jason mailed him a letter before his death. You could T a the acting classes in T world and it's not going torepare you for that. Very nervous. Theesays, if something were to happen me, please send this in aew weeks, do not open it. And there's an envelope in there with no rn address. To the iron river police department. It's like I'm supposed to mail this, but I wanted tell you. Uhh -- ple don't. You hear her wit this big sighd then she kind to suck it back UND gainomsure again. The next thing yno it's, dowhat you hav do. Reporter: Kelly Cochran immediately reaches out to detecti Ogden. She'ea to drop aombshell about Chris Regan's disappearance. What happened? Happened?how? What did he do withchris? Cut him up. Eporter: Kelly cs that her husband shot Chris Regan as pa of marriage pact the couple made. Finallyot her to admit that, you, S lured Chris re to the house. She said that her and Jason had this pac the night of their wedding, if oneatedn the other, that it was the responsibility of the one W cheated to kileir R. Kill them. Reporter: Eventually Kelly I arrested. Po look T her to helpind the body. Help Chris home.it something of Chris' so his kids can bury him and have a proper service. Reporter: Kelly agrees chief Laura Rizzo to where his bodyartsre buried andhere theader dog detects the scent ofuman remains on astic bag. I would say probably 600 RDS so from where that bag was found ultimately the dog ends up his openld and there's T skull laying right in the middle oe D. Hat was that moment like for you? Inribable, .I felt like -- for ainute like -- you know, is this really happg? Is iteallyim? I mean, you're just kind O thinking, I've been looor so long and ting I'm never going to find him. Cochran ishargedh homicide in connection T Regan's death -- eporter:ly Cochran standshris Regan's murder. Guilty. I felt guilty foris not beingere and prevent that Reporter: She is convic Kellyhran guilty on all S -- Reporter: Later pads guilty to killingerhusband, Jason. But both chief Rizzo and detective Ogden, who interviewed her many times, believe Kelly might be guilty uch more. Do think she's responsible for more than two murder Absolutely the way she controlherself, theducation she gave herself do the things and get away th them. You think she's a serial killer? Ow many people? I't know the . It's not as G as what she's claimed. She claimedone time she killed 21people. Reporter: Kelly Cochran is nowerving a lifesentence. Jail for ? Ever. How do you feel about that? I'm very glad the's there. And I mean -- T's others like her there. But at least Shean't hurt anyone . Reporter: For "Nightline," M linsey davn New York.

This transcript has been automatically generated and may not be 100% accurate.

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