It was an early May morning in 2005, and Patricia McDermott had no reason to expect anything but a typical commute to her job as an X-ray technician.
Riding the No. 33 bus through the predawn streets of Philadelphia, McDermott got off at her regular stop -- the post office on the corner of Ninth and Market streets.
She began walking south, toward Pennsylvania Hospital, but she never made it to work. Minutes after she got off the bus, McDermott was discovered lifeless on the street by a passing driver.
Police on the scene were stumped at first. Was it a robbery, an accident or a suicide?
"There was blood on the sidewalk," said Howard Peterman, one of the first detectives to respond. "We looked around for evidence for weapons. No ballistic evidence. We looked up to see if she had jumped from the building. … [There was] no evidence to show us what had happened."
But Peterman noticed something else when he looked up -- surveillance cameras mounted all around the post office.
Americans have grown accustomed to being filmed as part of their daily routines -- cameras are commonplace at ATMs, convenience stores, gas stations and building lobbies.
It's not so unusual anymore for those cameras to catch criminals in the act. But as the number of surveillance cameras increases, it seems not even random crimes on deserted streets in the dark of night can escape.
The footage from those post office cameras would be crucial to investigators as they pieced together exactly what happened to McDermott.
Federal agents showed Peterman the recordings from that morning. One camera captured McDermott, 48, getting off the bus. A man wearing a light jacket and dark pants got off the same bus, and followed a few steps behind her.
Another camera caught them as they rounded the corner. McDermott didn't seem to notice the man following her. Halfway down the block, the man suddenly raised his arm and shot her once in the back of the head.
"I've seen shootings incidents on video before," Peterman said, "but the suddenness, and that he did it for no reason at all, was really scary."
It was scary for the police, but devastating for the McDermott family. "I feel like my soul was shattered in two," said McDermott's sister Mary Moran, "like a windshield that's together but in pieces."
The seemingly senseless, cold-blooded murder of a beloved mother stunned the entire city of Philadelphia.
"There was shock, dismay. People were afraid. Immediately we think, 'Wow, this could happen to anybody, anybody,'" said Deputy Police Commissioner Richard Ross. "And we had to move quickly to find out what happened."
The cameras above the post office were installed by the Department of Homeland Security as part of an effort to beef up security around federal buildings. The cameras, made by Canadian company Extreme CCTV, are very sophisticated.
They are not only sensitive to light, but also emit infrared rays that can make night look virtually like day.
Still, there were limits to what detectives could glean from the cameras. Though the images were good, the angle wasn't. The cameras are high above the street to catch possible truck bombs, not individual faces. And the killer wore a baseball cap that further obscured his identity.