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.
The post office cameras showed police what happened to McDermott, but not who did it, let alone why.
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.
In a written statement to police, he said he had to kill McDermott because she was poisoning him with X-rays.
"I could feel the radiation when I went into the room," he said. "That's when I came to the conclusion that nobody would believe me about what she was doing to me."
It was an explanation that left McDermott's family members scratching their heads.
"To me it's a little ridiculous," said Angela Amarhanov, McDermott's daughter. "Honestly, it blows my mind that someone thought that my mom had a mean bone in her body, and that she would be capable of doing evil things."
Added Moran: "I hate to say that he's crazy. Because to me he was very calculating, and he had a gun, and he went up and he shot my sister in the head, very cold-bloodedly."
There were still more bombshells to come.
Before police closed the case on McDermott's murder, Covington admitted to having still more victims. He was no ordinary killer; he was a serial killer.
Two months before McDermott was gunned down, Covington shot and killed Odies Bosket, 36, at the Logan station of the Broad Street Subway line.
Bosket, a father of four, was on his way to pick up his 3-year-old daughter from nursery school.
In 1998, Covington murdered his cousin, the Rev. Thomas Lee Devlin. Devlin, 49, died in a hail of bullets as he was leading a prayer service in his sister's home.
In 2003, Covington jumped out from between two parked cars and shot David Stewart nine times as he walked home. Stewart, 43, miraculously survived.
In 2004, Covington also shot William Bryant, 33, as he walked to work. After shooting him several times from behind, Covington stood over the injured Bryant and fired two more shots. Like Stewart, Bryant was shot nine times and also survived.
Covington pleaded guilty but mentally ill to all these crimes, receiving a sentence of three life terms in prison and bringing to an end a one-man crime spree that spanned eight years.
"We are just glad that justice was brought to us and that he's not gonna be able to hurt anyone else," Amarhanov said outside the courthouse after Covington was sentenced in March.
Amarhanov now lives with Moran, who had promised her sister that she would take care of her children should anything happen to her.
"I know she'll be happy when she knows that we are doing so well or we are trying to do well," Amarhanov said.
Ironically, the video that showed her sister's murder also gave Moran some peace of mind, because it showed that her sister's last moments were not filled with fear.
"When I would watch it, I didn't sense that she was scared," she said. "She was just walking normally."
For law enforcement, the value of surveillance cameras could not be underscored enough.
Said district attorney Abraham: "McDermott's case might never have been solved. Who knows how many more victims there would have been had we not had that image of Covington murdering Ms. McDermott right on our video screens."