Police laid a trap to arrest Sheila Keen Warren, who allegedly dressed as a clown to kill her paramour's wife in 1990

Police were able to catch an alleged killer who police say dressed as a clown and killed a woman in Florida nearly 30 years ago by setting a trap for her, ABC’s 20/20 reports in an episode airing Friday night.

In May 1990, when Marlene Warren, 40, opened the door of her luxurious Palm Beach County home, she was fatally shot in the face by someone dressed as a clown who then slid into a white convertible and calmly drove away.

The case went cold for years until Palm Beach County authorities reopened it — and discovered new DNA evidence allegedly linking a woman named Sheila Keen Warren, 54, to the crime, say police.

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Sheila, they learned, is now married to Marlene’s widower, Michael Warren, 63, the man with whom she was rumored to have been having an affair at the time of the killing, say police.

Sheila and Michael lived for more than a decade in an upscale Abingdon, Virginia, neighborhood, where everyone knew them as “Debbie and Mike,” police say.

“They sort of flew under the radar,” Washington County Sheriff Fred Newman tells ABC correspondent Deborah Roberts in an exclusive clip 20/20 shared with PEOPLE.

Sheila Keen Warren
| Credit: Palm Beach County Sheriff's office/Palm Beach Post via AP

Their quiet life ended on Sept. 26, when police arrested Sheila in Abingdon, after setting a trap for her, Newman tells Roberts.

Police surveilled the Warrens, watching as the couple pulled out of the driveway of their French Tudor home in a black Cadillac Escalade, lying in wait for them when they returned.

“Vehicles were strategically placed along various locations and observed the black Cadillac Escalade as it was traveling,” he says.

After pulling over the SUV, police surrounded it and took Sheila into custody, and “Debbie’s” sedate life was over.

Sheila, who is seen smiling in one of the pictures taken by police, showed little emotion, he says.

“I did not notice anything from a standpoint of being distraught,” says Newman. “Somewhat surprised, I guess, if you would. But reasonably calm for the most part.”

Sheila was charged with first-degree murder and later extradited to Palm Beach County, where she awaits trial and faces the death penalty.

Sheila’s attorney has said she is innocent.

Friday night’s episode also includes interviews with Marlene’s mother and stepfather — as well as an exclusive interview with two women who may have unknowingly helped the alleged killer in her plot.

“Two former costume shop workers who say it’s likely that they sold the costume to the alleged killer sat down to discuss the case with me for the first time,” says Roberts in an exclusive statement to PEOPLE.

“They say they’re still pained by the idea that they may have [allegedly] unwittingly played a role in this awful murder,” she says.

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The episode also includes interviews and reporters who covered the crime and neighbors who know Sheila as “Debbie.”

20/20 airs on Friday, October 20, at 10:00 ET on ABC.