September 16, 2016 02:05 PM

More than two years after the July 2014 execution-style shooting of Florida State University law professor Dan Markel in the garage of his Tallahassee home, police are still investigating whether his ex-wife’s family had something to do with the killing.

In an exclusive clip from an ABC News 20/20 special airing Friday night, an undercover officer is seen approaching Donna Adelson, the mother of Markel’s ex-wife, Wendi Adelson.

The officer poses as the brother of one of the men arrested in Markel’s murder, 33-year-old Luis Rivera, and asks the woman for payment for Rivera’s alleged services.

“I want to let you know that my brother, he helped your family with this problem you guys had up north,” the officer, dressed in casual clothing, tells Adelson. “He’s going through some rough times and I want to make sure that you take care of what he’s going through.”

Undercover officer (left) and Donna Adelson

Adelson appears confused, and tells the man that she didn’t know what he was talking about.

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Along with Rivera, 34-year-old Sigfredo Garcia was arrested and charged in Markel’s death. Both have pleaded not guilty and are expected to be tried in November.

However, investigators asserted that Rivera and Garcia’s alleged involvement in the murder is just the tip of the iceberg, according to probable cause affidavits obtained by PEOPLE.

Dan Markel
Florida State University College of Law

Investigators have pointed a finger at Charlie Adelson, Wendi’s brother, alleging that he, Rivera and Garcia are “responsible for the murder of Daniel Markel.”

The affidavits allege that Charlie Adelson had previously looked into hiring a hitman and that a person connected to Garcia began receiving checks from the Adelson family’s dentistry practice after the killing – and that Rivera and Garcia purchased several cars and motorcycles.

However, State Attorney William Meggs told the Tallahassee Democrat that officials would not move forward against Charlie because his involvement cannot be proven.

“My opinion after reading those documents is there is no probable cause here to make an arrest,” he said.

“We kind of believe they were involved according to the police. But what we believe and what we think doesn’t count. What evidence do we have?”

Charlie Adelson’s lawyer commended the prosecutor’s decision.

“Mr. Meggs has spent the past 40 years as a prosecutor, with 30 years as State Attorney, and before that was a decorated police officer,” attorney David Oscar Markus told PEOPLE in a statement. “He is one of the most experienced State Attorneys in the nation and he knows probable cause when he sees it. We are thankful that he faithfully and honorably fulfilled his duties and did not approve this document, which amounted to no more than simple speculation after a truly exhaustive investigation.”

20/20‘s “In-Laws and Outlaws” special airs Friday (10 p.m. ET) on ABC.

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