The message on Rodney Bradford’s Facebook page, posted at 11:49 a.m. on Oct. 17, asked where his pancakes were. The words were typed from a computer in his father’s apartment in Harlem.

At the time, the sentence, written in street slang, was just another navel-gazing, cryptic Facebook status update  meaningless to anyone besides Mr. Bradford. But when Mr. Bradford, 19, was arrested the next day as a suspect in a robbery at the Farragut Houses in Brooklyn, where he lives, the words took on greater importance. They became his alibi.

His defense lawyer, Robert Reuland, told a Brooklyn assistant district attorney, Lindsay Gerdes, about the Facebook entry, which was made at the time of the robbery. The district attorney subpoenaed Facebook to verify that the words had been typed from a computer at an apartment at 71 West 118th Street in Manhattan, the home of Mr. Bradford’s father. When that was confirmed, the charges were dropped.

“This is the first case that I’m aware of in which a Facebook update has been used as alibi evidence,” said John G. Browning, a lawyer in Dallas who studies social networking and the law. “We are going to see more of that because of how prevalent social networking has become.”