Procopio was last seen Sept. 24, 1999, leaving her job at QVC in West Chester, where she worked in the accounts-payable department.
Her red 1990 Pontiac Sunbird coupe was found Oct. 7 in Bridgeport, Montgomery County. It was legally parked, an antitheft device was attached to the steering wheel, and the seat was set all the way forward, suggesting that someone her size was the last person to drive the car.
The case took a lurid turn when it became public that Procopio was secretly known as "Mistress Maria," a dominatrix with a phone-sex line and numerous clients.
Thomas became a suspect when he was first questioned. He reluctantly agreed to show police his Center City apartment, but when they got there, he tried to run away. He was tackled by police, who then searched his apartment, believing Procopio might be inside.
Instead, they found counterfeit cash, numerous phony IDs, night-vision equipment, and texts on how to commit scams.
Thomas was sent to federal prison in 2000 for counterfeiting but was not charged in the disappearance of Procopio, who was never found.
Philadelphia Police Capt. Frank Vanore, who worked on the case as a sergeant, said Thomas was investigated thoroughly after the disappearance.
"He was interviewed several times," Vanore said. "But one of the biggest problems was that we never found her, not a trace."
Police could never link Thomas to Procopio's disappearance, Vanore said.
"We took it as far as we could at the time," he said.
Teresa Camino, Procopio's 52-year-old sister, is convinced Thomas was involved.
"I have no doubt in my mind," Camino said.
"He's never been up-front and truthful" about what happened to Procopio, she said.
Procopio was declared legally dead in 2006, Camino said.
With Thomas dead, Procopio's vanishing may never be solved.
Camino said the focus should be on the fallen officer.
"Our thoughts and prayers are with his family," she said.
Contact Robert Moran at 215-854-5983 or email@example.com, or follow @RobertMoran215 on Twitter.
Inquirer staff writer Allison Steele contributed to this article.