Last week a 39-year old man was shot in a Queens barbershop by a man wielding a sawed-off shotgun known by the nickname "Armani." The victim's brother, who was present at the time, told detectives that although he didn't know the shooter's real name, he could probably find some pictures of him on Facebook.
He did just that, and passed the images to Sgt. Michael Ackerman, who forwarded them onto the NYPD's Real Time Crime Center, a 21st century-style crime database that can search images based on facial-recognition software known as "faceprinting" (no, not that). A few bells and whistles later (a search through thousands of mugshots), and the top hit was identified as Jordan Rodriguez, a 37-year old with an arrest record with assaults that took place right near the scene of the crime. Police found Rodriguez hiding out at his sister's house a few days later. Nabbed!
According to various news reports, the sophisticated face-recognition technology ultimately delivered the perp to the cops, but this is overlooking the most important part: this criminal had his pictures posted on Facebook, and the brother of the guy he shot knew where to look for them.
Sociologically, whether it speaks about crimes being committed by people in the same social circles is secondary; it's the never-ending photographic life-documentation of Facebook that is important—Facebook is always watching.