PHILADELPHIA -- Most people post what they ate for lunch, brag about their kids or lament a slow workday on their Facebook status.
Omar Woods of Kensington confessed a crime: "I'm on da run for 3 attemed [sic] murders."
That status update, along with photos that Mr. Woods later posted of himself with a handgun jammed in his waistband, now could help convict him in a July shooting in Kensington that injured three people.
As social-media use grows, more suspects, like Mr. Woods, are posting incriminating information or photos online. Some brag about misdeeds to improve their social standing or intimidate enemies. Others, lulled by the Internet's illusion of anonymity, never dream that police could pick out their posts from the sea of cyber data.
But the trend has proved to be a windfall for law enforcement, which now has another tool to tackle crime.
"One of the great things about the Internet is it gives people a voice," said Cpl. Frank Domizio, a Philadelphia Police Department social-media specialist. "And if your voice is not that smart, it gives you a voice that's going to get you arrested."
Drexel University criminologist Rob D'Ovidio agreed: "Think of it as a high-tech version of a stakeout. They can gather intelligence and evidence essentially by spying on suspects online."
Such tactics helped police in South Jersey crack the case of Autumn Pasquale, 12, who had traded messages and meet-up plans with her alleged killer on Facebook, days before her disappearance and murder, about their mutual interest in motocross bikes.
Last fall, when two teens burglarized a Northeast Philadelphia man's apartment, a neighbor's security camera caught a clear picture of them. Facebook helped investigators identify one suspect after she posted a photo of herself, the day after the Nov. 11 burglary, in the same blue plaid shirt she'd worn in the burglary, according to court records.
In Woods' case, he made his "on da run" post 12 days after he allegedly shot three people July 23 at G Street and Allegheny Avenue, according to court records.
The victims had come to the corner hunting for a friend's stolen cell phone. But when they asked teens gathered there about it, a fight erupted, ending with a gunman opening fire, court records show. One victim caught a bullet in the armpit; the other two were shot in their legs. One remains in a wheelchair after multiple surgeries, records show.
Mr. Woods, 19, was a suspect early in the probe, and witnesses later identified him as the shooter, court files show. In November and December, he posted photos of himself on Facebook with guns in his waistband -- including a semi-automatic pistol similar to the 9 mm used in the shooting, according to court records.
Prosecutors have taken the case to a grand jury, claiming witness intimidation, said Joshua Scarpello, Mr. Woods' attorney.
Both Andrew Wellbrock, the assistant district attorney prosecuting Woods, and Tasha Jamerson, a spokeswoman for the district attorney's office, declined to comment on the Woods case or on how police and prosecutors mine social media for evidence.
But experts have plenty of theories about why vanity often trumps self-preservation on social media.
"There's a perceived sense of anonymity online that leads to a false sense of security," said Mr. D'Ovidio, associate professor of criminal justice at Drexel and an expert on high-tech crime. "People figure, 'There's so much info out there that police aren't really going to find my Facebook postings of my exploits with guns.' "
In Autumn Pasquale's case, investigators discovered that Justin Robinson, 15, had invited the young girl from Clayton, N.J., to visit his house after the two discussed BMX bikes on Facebook Oct. 16.
On Oct. 21 -- the day after Autumn vanished -- Justin "liked" a Facebook page that was devoted to finding the girl. But that same day, he also had a bizarre Facebook exchange with Autumn's brother, A.J.
Justin Robinson posted a message that read in part: "it was an accident the cop waz here & my brother did it."
Autumn's body was found in a recycling bin near Robinson's home on Oct. 23. Justin and his brother, Dante, 17, were charged with her murder.
Some criminals, however, purposefully post incriminating information.
"They're doing what they think is necessary to evolve and to ascend, and that includes immortalizing dumb criminal behavior," said Chuck Williams, associate professor of psychology and education at Drexel and founding director of the Center for the Prevention of School-Aged Violence. "It seems crazy to us, but in their world, it gives them a certain level of respect."
Posting tough talk and photos of weapons also can discourage enemies and competitors, Mr. Williams said.
"It's like a tiger showing its teeth or a dog growling when it feels threatened," he said. "It's a pre-emptive strike, an announcement: 'Just in case you didn't know, I have guns and I will use them.' "