The 21st century update of the old saw where the burglar leaves his wallet in the sofa cushions:

The popular online social networking site Facebook helped lead to an alleged burglar’s arrest after he stopped check his account on the victim’s computer, but forgot to log out before leaving the home with two diamond rings.

While this particular breed of clumsiness is of course quite rare, according to a friend of mine who is a cop, it is becoming standard practice in certain kind of crimes to check the suspect’s public Facebook profile.

The default settings on Facebook show a limited version of someone’s profile, but also show with whom they are friends.  So suppose you’ve just arrested some kid who knocked over a 7-11.  From witnesses, you know he had help.  But who could have been his associates?  The friends list in some cases is an exceedingly helpful starting point.