For more than 30 years, the “killer clown” has captivated investigators, Floridians, and true crime fans all over the world.

A clown who approached Marlene Warren’s door and gave her balloons and flowers shot and killed her in front of her son.

While the terrifying situation made headlines at the time and remained a major unsolved mystery for a decade, Warren’s son Joey Ahrens revealed in an exclusive interview with “20/20” that it left a hole in his heart that has never been filled.

“She was a great mother,” Joe Ahrens said in an exclusive interview with “20/20.” “She had a lot of charisma.” She was a loving person.”

Nearly six years ago, investigators announced a breakthrough in the case, claiming that new DNA evidence from mysterious hairs found in the getaway car and other clues pointed directly to Sheila Keen Warren, Ahrens’ stepfather’s second wife. Last week, she pleaded guilty to second-degree murder.

“I never thought I was going to get a guilty [verdict],” Ahtens said on “20/20” after the sentencing. “Wow, that was unexpected. It completely blew my mind.”

According to investigators, Marlene Warren was at her Wellington, Florida, home on May 26, 1990, with Ahrens, who was 21 at the time, and several of his friends. She was living with her second husband, Michael Warren, who ran a used car lot and a rental car agency at the time.

Ahrens stated that he, his friends, and his mother witnessed a white Chrysler LeBaron pull into the driveway shortly before 11 a.m. that day, and that a clown appeared at the front door with flowers and balloons.

According to police, one of the balloons said, “You’re the Greatest.”

“The last words I heard my mother say was, ‘Oh, how pretty,’ and bang,” Ahrens said.

According to witnesses, the clown fled in the car, and Warren died two days later in the hospital.

Police were able to track down the stores where the balloons, flowers, and clown costume were purchased in the immediate aftermath of the murder, and Deborah Offerman, a store employee, told investigators that she remembered selling the clown costume, wig, and other accessories to a woman who came into the store right before closing.

“‘I need to buy a costume,’ she said, and I asked, ‘Can you come back tomorrow?'” “We’re closed,'” Offerman told “20/20” in 2017. “‘No, I need this tonight.'” “I need to get a costume tonight,” the customer said.

Four days after the shooting, officers were alerted to an abandoned Chrysler LeBaron in a Winn-Dixie parking lot. Inside, they discovered “trace evidence,” such as artificial orange-like fibers that could have come from a clown wig, according to law enforcement officers.

They also discovered what appeared to be long brown strands of human hair, which proved crucial later in the case.

DNA analysis was not as advanced at the time, and relevant DNA could not be extracted from hair.

Despite being questioned by police, Michael Warren had an alibi because he was on his way to a Miami racetrack with friends at the time of the shooting. He denied any knowledge of the murder.

Friends and family told police that Michael Warren may have been having an affair with his employee Sheila Keen, who was a repossession agent.

Investigators questioned Keen and Michael Warren about the affair, but both denied involvement.

Employees at the costume shop identified Keen Warren as the woman who purchased the clown suit. Cops searched her house but discovered no evidence to warrant an arrest.

Unbeknownst to most of their Florida friends and family, Keen and Michael Warren would marry in 2002 and relocate to Virginia. Meanwhile, investigators were unable to uncover any new leads in the case.

Ahrens claimed that the pain of his mother’s death, as well as the fact that his family was denied justice, drove him to depression and alcoholism.

He eventually entered rehab and claims that his mental health has improved.

“I broke down, and I said, ‘Enough is enough, I can’t do this on my own,'” he explained.

When new prosecutor Reid Scott revisited the forensic evidence discovered during the initial investigation in 2013, the case gained traction.

Scott directed that the hairs be tested using mitochondrial DNA analysis, which he described to “20/20” as a “type of analysis that is typically conducted on older samples.”

According to investigators, the more advanced analysis determined that the hair matched Keen Warren.

In October 2017, she was arrested and extradited to Florida on charges of first-degree murder in the death of Marlene Warren.

Michael Warren was not prosecuted.

Keen Warren sat in jail for five years while her attorney, Greg Rosenfeld, maintained her innocence and questioned the prosecutors’ case.

Rosenfeld told “20/20” that the validity of DNA evidence and analysis was called into question because it had been in storage for so long.

He also mentioned that Aherns and other witnesses initially claimed the clown was a man.

“A clown costume will not conceal your gender. “Even with makeup on, you can tell if a clown is a man or a woman,” he said.

Scott, on the other hand, stated that the clues added up.

“Yes, it’s circumstantial evidence,” he said, “but it’s an overwhelming amount of circumstantial evidence.”

Meanwhile, Ahrens stated that he was confident Keen Warren would face justice.

“My mother was murdered by Sheila Keen-Warren.” I was present, and I saw her eyes. And I’ll explain. They serve as the eyes. “They’re people I’ll never forget,” he said.

But, just a few weeks before the trial, Keen Warren made an unexpected announcement: she was going to negotiate a plea deal with prosecutors.

The deal, which was announced on April 25, had Keen Warren plead guilty to second-degree murder in exchange for a 12-year sentence. Rosenfeld said that her five and a half years in custody would count towards that sentence and she could be released next year on good behavior.

“The defendant is pleading guilty because she is guilty and there is a factual basis for the crime,” Scott explained.

At the plea hearing, Ahrens appeared via video conference and told the judge that he accepted the conditions but never saw Keen Warren show remorse.

“My final conclusion was that I would be content with the outcome,” he said. “Guilty or not, I was going to be okay.”

A few days after the plea deal was finalized, Ahrens visited his mother’s grave to give her a message.

“I was telling her we finally got truth. We finally got closure,” he said.