Accused Hitman in FSU Prof. Murder Case Cooperating with Authorities

One of the men accused of killing Florida State University law professor Dan Markel "flipped" and has now pleaded guilty to murder charges.
7:14 | 10/07/16

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Transcript for Accused Hitman in FSU Prof. Murder Case Cooperating with Authorities
We turn now to a twisted murder plot the case of a Florida College professor gunned down by a hit man but who hired him. After two years authorities say there are finally unraveling the mystery here's ABC's Matt cut. And it was a sensational murder case and mysterious killing of a prominent law professor who murdered execution is now a mystery assassination. Of renowned Florida state university law professor Dan Martin Cahill and but now a stunning turn them or you could call it a flick. Werner K please what. One of the two hit men accused of killing the professor Luis Rivera is now cooperating with the prosecution. And understand what. The man who clammed up for months has now opened up. Talking with prosecutors in exchange for a vastly later sent its. Prosecutors say Rivera and his accomplices secretive Garcia who were high your forty alleged game it was July 2014 when mark hill was shot. Twice in the head in the garage of his Tallahassee home. He's inside the car running he's got blood all holders here at. But who called the beloved professor dead. These beautiful ex wife Wendi Adelson also at this U law professor told the police did not everything has been amicable when their divorce. Consular you. You Wendy's boyfriend at the time told police that her family had come to hate mark kill for blocking Wayne. Their family. Desperately wants her back and South Park mother father. And she has a rather. They hate me in a way. Never seen this kind. Session. What was that reason enough for her family he got a kid on the professor. As police begin they discovered that ate food a preconceived leaving the scene of the crime and directed by a member of the notorious Latin kings game. You may remember his name. Luis Rivera. According to police this surveillance video showed. Following the professor neatly fit this in her on the morning of the killings and David real name on his eventful. Police say that later that evening a big security camera captured Rivera if he's accomplished in the Prius back in Miami. Withdrawing money for many TN blue. This may Rivera and his accomplice Siegfried who Garcia were charged with first degree murder mark yells killing and both pleaded not guilty. But everybody's asking who hired them prosecutors say Rivera's plea deal this week may be the key to solving that mystery and well worth the lighter sentence I'm. San last past six farmers trying to hold everyone accountable. As part of its kind. She's just there is frustration has already led to be rests just last weekend of this key suspect Catherine nag but you. The link between a hit man and windy eagle since well heeled family. Meg wonder what is the mother of accused hit man Garcia his two children. And get this she's also the girlfriend of Wendy's brother are surely. Dean Charlie Adelson had anything to do with mark hill's murder. No he's being looked act because of the fact that he any dating relationship. We've Catherine however. There is no evidence that he solicited any type of murder non. But according terror arrest affidavit police believe the murderer was arranged through mag but knew what and did she made cash deposits of over. 56000. Dollars and sixty months following the murder. Police also say an informant told them the child Beatles and picked up half that's bad for a pricey breast job meg avenue and got just. Three months after the murder. Police say that Rivera who was incarcerated on an unrelated charge and told someone almost flown to nag but knew ahead all the money and then she needed to be nice to him and give him bail money armed with that tidbit of information. Like or police set up an elaborate sting this April. Dean didn't rattling the Eagles six were happily reunited with Wendy and the two kids in South Florida. But watch what happens when done and he's a little. She's in for allegedly undercover agent posing as police Rivera's brother. Here's the agent Chris is got a prepayment for services rendered by his. Brother of weeks. Behavior their walk away. Police say inside that envelope is he press release about kmart's sales murderer aid fund over its demands for 1000 dollars. So how would the grandmother react. Low. They're protected fatal and Nightline exclusively obtaining this recording of Donna it'll since call back to that undercover agent. Three weeks after the state. I don't know your friend who is in jail sorry your friend enjoy L but I don't know. What that have to do with me. You know exactly what discussion with you told me everything I'm our callers who who fell on the part of pay. Everybody knows what's going on. I got you know you're saying everyone knows I know I lost my external law he did not. Had anything. To do with it. I needles and sticks to her guns. And immediately denying any knowledge of a plot but police say the ruse and still war. Donna's call followed a series of movies conversations between the Eagles since nagged Motorola and the alleged hit dancing Prado Garcia. Police say be discussed paying out of five grand. Would never do. And according to police documents show Orly Adelson Whitney's brother allegedly told backed into a that he wanted that mysterious messenger eliminated. Permanently saying you better kill him because he's going to be a big problem if you can't do it I'll have someone else. Police had heard enough. This may be submitted arrest affidavits for Charlie Adelson and Keaton meg but new stating they were responsible for the murder of Daniel mark Cahill. But at the time the prosecutor declined to file charges citing. Insufficient evidence when ABC news recently caught up with Charlie tells NBC closing eager to answer our questions. Doctor Alison. Beautiful for the plots to kill itself. Where the shooting did you ever discuss hiring a hit man. Attorneys for beetle since it said the accusations of their involvement are nothing more than fanciful fiction. And in response to Rivera's plea deal Charlie Wilson's attorney Sidney hit man who would say anything to avoid the death penalty. But with Rivera now cooperating and back renewal in custody prosecutors want to turn that. Hope of future arrests into reality. For Nightline I'm Matt governing in Tallahassee Florida.

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

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