A pivotal trial in one of the most sensational murders in Florida in the last decade has quietly gotten underway in Tallahassee, where a flashy dentist from a prominent Miami Jewish family is on trial for hiring hitmen to kill his former brother-in-law.

The trial of Charlie Adelson is the latest chapter in the case of the murder of Dan Markel, a celebrated law professor with two Harvard degrees who studied punishment in the criminal justice system, with a focus on the role of family. Ironically, in 2014, Mr. Markel became a victim of a murder that prosecutors say was very much in the family. He had just gone through an acrimonious divorce when he was gunned down while sitting in his car outside his modest house in Tallahassee. 

Prosecutors allege that Mr. Adelson, Mr. Markel’s former brother in law, hired hit men from the Latin Kings to kill Mr. Markel because he was blocking his ex-wife Wendi from moving from Tallahassee to Miami with their children. For years, prosecutors and detectives had circled Charlie Adelson and his wealthy family, who own a successful dental practice. Mr. Adelson was finally arrested last year and charged with first-degree murder, conspiracy and solicitation. 

“The reason that we’re here today is because the defendant in this case, Charlie Adelson, hired a hit man to kill his former brother-in-law, Dan Markel,” Assistant State Attorney Kathryn Dugan said. “This murder was set into motion because back in 2014, the defendant’s family, the Adelson family, had a big problem. And that big problem was Dan Markel. This defendant was the solution to that problem because he had a girlfriend with connections to the type of people who were willing and capable of pointing a gun at a complete stranger and pulling the trigger.”

The motives for the murder, prosecutors say, were twofold. One was that with Mr. Markel dead, Wendi Adelson could move with their children to Miami, which a judge had forbade her from doing due to Mr. Markel’s tenured professorship at Florida State in Tallahassee. The second motive was a legal motion Mr. Markel had filed to keep his former mother-in-law, Donna Adelson, “from having unsupervised contact with her grandchildren.” 

“The murder of Dan Markel ensured that an adverse ruling on his motion would never be a problem for the Adelsons,” Ms. Dugan said.

The two hitmen, Luis Rivera, a high-ranking member of the Latin Kings and his friend Sigfredo Garcia, have both already been sentenced to prison. Rivera took a plea deal for 19 years behind bars, while Garcia was found guilty at trial and sentenced to life. Prosecutors then turned their attention to Garcia’s common law wife, Katie Magbanua, the mother of his children. Magbanua, a cocktail waitress, was dating Charlie Adelson. 

Magbanua refused to flip on the Adelsons, much to the frustration of prosecutors. She was tried twice for murder: the first trial ended in a mistrial, the second in a conviction, resulting in a life sentence. It wasn’t until Charlie Adelson was arrested that Magbanua,  facing the rest of her life behind bars, changed her tune. On Monday, she testified in detail against Mr. Adelson.

“I believe that the truth needed to come out now so that the family can get some type of closure,” Magbanua said when asked why she finally agreed to testify.

Magbanua claimed that Mr. Adelson came up with the idea for the murder, asking her in 2013 if she knew “anyone that can harm someone,” to which she replied, yes. She told the jury that Mr. Adelson gave her a sealed envelope – which she believed included Mr. Markel’s picture and address – to pass on to Garcia. Mr Adelson told her, she testified, not to open the envelope.

Magbanua also helped prosecutors by authenticating transcripts from the voluminous secret recordings that law enforcement had made of her and Mr. Adelson, including at restaurants, and translating the code language she used with her boyfriend. She admitted receiving money from the Adelsons for a no show job at their dental clinic, spending some of it on breast augmentation.

Mr. Adelson’s lawyer, Daniel L. Rashbaum, denied his client’s involvement in Mr. Markel’s murder and pointed the finger squarely at Magbanua. He argued that Magbanua concocted a plot to extort money from the Adelsons when she learned they were so desperate for their daughter and grandchildren to move to Miami that they were going to offer Mr. Markel one million dollars to let them go.

“You will learn that Katie heard about the million-dollar offer and got some ideas in her head,” Mr. Rashbaum said, arguing that Magbanua decided to orchestrate the murder on spec in hopes of a big payday. “The state has called Katherine Magbanua the mastermind, and that’s exactly what she was.”

A day after the murder, the defense claims, Magbanua came to Mr. Adelson and told him that an unnamed friend of hers had killed Mr. Markel and that another Adelson would be next if he didn’t hand over the money within 48 hours.

“She said she had nothing to do with it,” Mr. Rashbaum explained. “She was talking too much. Her friends learned about the problem that his family was having with Professor Markel. They learned about the million-dollar offer. They got it in their minds to do this.”

Mr. Rashbaum also claims there was bad blood between Mr. Adelson and hitman Sigfredo Garcia, who has two children with Magbanua.

“The shooter of Professor Markel, the man who murdered him, hated Charlie Adelson,” Rashbaum said. “And he calls him and he threatens him. He tells him if you keep dating Katie, we’re going to go mano a mano, I’m going to kill you.”

Mr. Adelson’s attorneys do admit that their client often repeated a “joke” saying he wanted hire a hitman to kill Mr. Markel, his sister’s nemesis. This jesting, they say, further encouraged Magbanua to pursue her schemes.

“Not only was it a bad joke, but you are going to hear that he repeated the joke, repeated it to a lot of people,” Rashbaum said. “You are going to hear that he repeated it as late as March 2014.”

The two Adelson women, Mr. Markel’s ex-wife Wendi and her mother, Donna, are co-conspirators in the case (along with husband and father Harvey Adelson) but have not been charged. Prosecutors have remained intent on charging Donna, who they claim was so intent on wresting her grandchildren from Mr. Markel that she contemplated threatening to convert them to Catholicism to enrage their father, an observant Jew, even though the Adelsons themselves are Jewish. During their pursuit of the Adelsons, prosecutors even did what’s called “a bump,” having a detective “bump into” Donna, pretending to be a Latin King claiming knowledge of the murder and trying to extort her. The hope was to goad Ms. Adelson into making a frantic call (on a wiretapped line) to her son and revealing her involvement in the murder plot. It didn’t work. 

Wendi Adelson has proven even more elusive. A lawyer herself, she testified smoothly last week that she had no knowledge of any plot to kill her ex-husband.

“Your family had your ex-husband killed to try to help you, right?” prosecutor Georgia Cappleman asked.

“No, that’s completely untrue,” she replied.

Charlie Adelson will take the stand in his own defense on Thursday.