9 years after the murder of a Florida law professor, a family gets justice

Nearly a decade after a Florida State University Law School professor was shot to death at his home while sitting in his car, his family said they are relieved.

On Monday, a Florida jury found Charlie Adelson guilty of concocting a plot with a former girlfriend and hiring two men to kill his former brother-in-law Dan Markel in 2014.

Markel's family had long suspected the Adelson family of being involved in the shooting, which took place while Markel and his ex-wife Wendi Adelson were in a bitter dispute.

"It's sort of tinged with this feeling of relief. It's really been a long time coming," Shelly Markel, the victim's sister, told reporters after the verdict.

A "20/20" episode airing Friday, Nov. 10, and airing on Hulu the next day, takes a look at the journey that investigators and prosecutors took to get to this week's conviction with exclusive interviews, and footage from the courtroom as the drama unfolded.

Markel had finalized his divorce from Wendi Adelson in 2013, but they were still in a dispute over personal property, finances and allegations from Markel that his former mother-in-law, Donna Adelson, was disparaging him during her visits with the couple's two young sons.

On July 18, 2014, Markel was found shot in the head inside his car outside his Tallahassee home and died less than 24 hours later in the hospital.

Tallahassee police interviewed Wendi Adelson, who told them about the divorce issues but denied that she was involved in the shooting. She allowed investigators to view her phone, swab her for fingerprints and photograph her.

As investigators searched for clues, they interviewed Wendi Adelson's former boyfriend Jeffrey Lacasse, who told them they should look into Wendi Adelson's brother, Charlie.

"[Wendi] told me that Charlie had looked into having Danny killed in the summer of 2013," Lacasse told police in a filmed interview. "She meant it dead serious. He said it would cost about $15,000."

Wendi Adelson told officers during her initial interview that her brother made a lot of jokes, including one about hiring a hitman. As the investigation continued, more evidence mounted that would implicate him.

Investigators began to probe the Adelson family and in April 2016, they staked out Donna Adelson as part of an undercover operation. During the sting, an undercover FBI agent wearing a recording device approached her claiming to be the brother of one of the suspects and demanded $5,000.

"He helped your family with this problem you guys had up north," the agent is heard saying to Adelson. "He's going through some rough times and I want to make sure that you take care of what he's going through the way you're taking care of Katie and Tuto."

"I don't know what you're talking about," Donna Adelson insisted.

The agent then handed her a press release of Markel's murder with a phone number to call.

Adelson then called her son, Charlie, in a conversation that was secretly recorded by authorities.

"Does it involve me or other people?" Charlie Adelson asked.

"Well, probably the both of us," his mother replied. "You probably have a general idea what I'm talking about. So let's just find some time to talk to each other."

In another undercover phone recording, Charlie is heard calling Magbanua, demanding to "find out who… it is and tell them to stop playing their games… I don't know who you have to talk to, but it needs to be nipped in the bud."

Though police thought the conversations were suspicious, it was not a confession

At the same time, investigators followed up on their only clue a neighbor's account of seeing a car that looked like a Prius speeding away right after the murder.

The police got a big break from surveillance footage from Markel's gym, a city bus and street cameras from the day he died that showed a green Toyota Prius following him as he made his way home.

Toll records for the car led investigators to a car rental agency in Miami. The rental agreement for the car showed that it was rented by a man named Luis Rivera.

Police said Rivera was a leader in the North Miami branch of the Latin Kings gang.

A second telephone number was also written on the rental contract with the word "Brother" written beside the number. That cellphone number tracked back to Sigfredo "Tuto" Garcia of North Miami, a childhood friend of Rivera who had a long criminal record.

Using cellphone data, surveillance video from buses, and GPS info, police said they were able to determine that the two men had been in the vicinity of Markel's home at the time of the murder.

In May 2016, police announced first-degree murder charges against Rivera and Garcia. Both entered not guilty pleas.

Investigators would then discover a personal connection between one of the suspects and Charlie Adelson.

Police looked into Katie Magbanua, who has two children with Garcia and who dated Charlie Adelson between 2013 and 2015.

Investigators found Magbanua collected regular paychecks from the Adelsons' family dental practice, Adelson Institute, signed by Donna Adelson.

According to investigators, there was no record of any work schedule or job title for Magbanua in paperwork subpoenaed from the dentistry business.

While the Adelsons carried on with life in Miami, Rivera was in prison on another charge when he approached prosecutors and offered information.

They came up with a plea deal: If he would describe his role in the murder of Dan Markel, and testify against his alleged co-conspirators, he could plead guilty and receive a significantly reduced sentence.

In October 2016, Rivera gave a statement to law enforcement claiming Garcia asked him to come along with him to carry out a hit and showed him a photo of Dan Markel.

"I asked him, who's ----- hiring me? He's like, 'Katie [Magbanua] told me this lady's going to hire me, but I want you to go with me. I'll give you $35,000.' I said, 'All right, for the drive? All right.' … Katie's the one in the middle doing everything. [Garcia] put it like that," Rivera told prosecutors.

"I asked him, 'Why are you going to kill this guy?' … [Garcia said] 'Because the lady wants her two kids back. She wants full custody of them kids,'" Rivera continued.

Rivera told prosecutors that in the summer of 2014, the two found Markel and trailed him for a few days. He said at one point, they followed him home and Garcia was the one who fatally shot Markel. . Rivera also told prosecutors the first person Garcia spoke with after the murder was Magbanua.

Magbanua was charged with first-degree murder and Rivera testified in her and Garcia's trials.

Garcia was convicted on Oct. 11, 2019, of first-degree murder and later sentenced to life in prison without the possibility of parole. The same jury that convicted Garcia couldn't agree on a verdict for Magbanua, resulting in a mistrial.

After years of pandemic-related delays, Magbanua was retried and convicted of first-degree murder, conspiracy, and solicitation to commit murder in May 2022. She was sentenced to life in prison and two additional 30-year sentences, to be served concurrently.

Investigators, however, continued to pursue leads into Charlie Adelson, and got a break when a 2016 secret recording between him and Magbanua was enhanced in 2022 by the FBI and produced more clear dialogue.

"If you're going to charge me, charge me," Adelson said in the recording. "They didn't mention my name, which makes me think – these people only know part of the story...or they think they know part of the story."

"If they had any evidence, we would have already gone to the airport," he added.

A Florida grand jury indicted Charlie Adelson on first-degree murder changes on April 20, 2022, and he was arrested the next day. He pleaded not guilty.

"I was shocked," Ruth Markel, Dan Markel's mother, told "20/20."

"It was unbelievable to hear. It was a relief because it's taken so long," Phil Markel, Dan Markel's father, told "20/20."

Adelson's criminal trial began last month and his defense attorney Daniel Rashbaum contended his client wasn't the mastermind, but instead was being extorted by Dan Markel's convicted killers.

Prosecutors brought back Rivera to the stand and he denied the allegations made by Rashbaum.

Magbanua also testified as a prosecution witness and, for the first time under oath, testified that Adelson orchestrated the plot and that she was involved with paying off the two men.

"So you knew that the person that was going to be initially harmed was Wendi's husband?" Florida Assistant State Attorney Georgia Cappleman asked.

"Yes ma'am," Magbanua replied. "[Garcia] painted this picture that this was a terrible man and making his family go through a lot custody-wise with his sister."

During cross-examination, Rashbaum questioned why Magbanua didn't come clean earlier and take a deal with prosecutors when they asked. She responded that she didn't want to give up the father of her children and denied any allegations that she blackmailed Charlie Adelson.

Charlie Adelson took the stand in his own defense and told the jury the prosecution's theory of the case was inaccurate.

"The state got it wrong," Adelson testified.

He testified that Magbanua came to him the night of Markel's murder claiming that a friend of hers killed the professor and was demanding Charlie pay a third of a million dollars within 48 hours or he, or another family member, would be killed next.

Charlie Adelson testified she wouldn't tell him who did it until months later when she claimed it was Garcia and Rivera.

"And I'm like, 'Katie, I'm not going be part of this s---. Like, I'm not going be part of paying for a murder. This is insane," Adelson testified.

Ultimately the defendant testified that he gave Magbanua $138,000 from his safe and paid her thousands of dollars more over the next couple of months claiming he asked his mother to put Magbanua on the payroll of the family dental practice.

During cross-examination, prosecutors questioned Charlie Adelson why he never went to the police with the information. He testified he was afraid for his life.

Cappleman also questioned Charlie Adelson on why he didn't testify at Magbanua's criminal trial.

"I thought the truth was going to come out," he said.

It took the jury three hours before they reached their verdict against Charlie Adelson.

A pre-sentencing hearing is scheduled for December. Adelson's attorneys have not immediately commented on any future appeals.

When asked if this was the last prosecution for Markel's murder, Cappleman told reporters after the verdict, "Stay tuned."

In the meantime, Markel's parents have lost years of time with their two grandsons, whom they rarely saw after investigators started probing the Adelsons in 2016.

"The first visit was incredible," Phil Markel said. "And we were shocked. The kids were smiling, they were warm."

"And I said, 'Can we give you a hug?' Ruth Markel said. "And they really responded."

"It's a spark of hope that something was going to happen, that we might have more communication with them," Phil Markel said.

ABC News' Allie Yang contributed to this report.