Detectives needed more clues. While there were no human witnesses to the killing, there were potentially dozens of mechanical ones. On nearly every block of downtown Philadelphia, a motley assortment of cameras watch over department stores, lobbies, storefronts, office and apartment buildings. So investigators went door to door, collecting tapes.
They found key footage from a camera in the parking lot across from the scene of the killing. That camera, unlike the post office cameras, recorded in real time.
"It solidified the fact there was no interaction between Patricia McDermott and her killer. There was distance between them, and they had no interaction," Peterman said.
That camera also captured the killer running through the parking lot as he left the scene of the crime, giving detectives a clue about the direction of his getaway. Other cameras caught him running down Market Street, and through an office building on Sixth Street.
Often, detectives had little more than a blip on the screen to work with, but those fleeting images were enough for them to piece together the shooter's escape route. It was painstaking work that did not go unnoticed by McDermott's family.
"I can't even imagine having to sit through and watch all those tapes, and how they tracked him just by the clothes that he had on and went from one spot to another," Moran said.
After looking at about 50 different video systems in the neighborhood, police captured the footsteps of the killer on at least a dozen different cameras.
They followed him for more than half a mile, to the corner of Sixth and Spruce streets, where the trail grew cold. The killer seemed to have vanished into thin air.
Unfortunately, none of the videos showed the killer's face clearly. Detectives turned to their in-house audiovisual unit, the District Attorney's Office, the FBI, even NFL Films, all in a vain attempt to enhance the images.
"They did what they could try to zoom in as much as possible. You just lost clarity the more you zoomed in on the lens," Peterman said.
There are some high-tech cameras in Philadelphia that can zoom in on faces. There are 10 such cameras in the city, mounted in a handful of high-crime areas as part of a pilot program that is monitored 24 hours a day by the police.
Unfortunately for the investigators on the McDermott case, the cameras had not yet come on line. So they hit the airwaves for help. Police released the images of the killer they had on tape, hoping that someone might recognize his clothes or how he walked.
That effort yielded hundreds of tips, including one that would become the big break in the case.
A bus company employee thought the man in the grainy image resembled someone she knew -- Juan Covington, who, like McDermott, was a regular rider on the No. 33 bus.
Covington, it turned out, had something else in common with McDermott. He too worked at Pennsylvania Hospital, where police found the last piece of the puzzle.
One of the hospital's surveillance cameras captured Covington entering the hospital less than half an hour after the murder.
"When we looked at the footage, and saw it was the same man wearing the same baseball hat, the same clothing, we knew we had our man," said Philadelphia District Attorney Lynne Abraham. "I mean, there he was, the guy. Our killer."
Confronted with the video, Covington confessed.