Factual error: In the beginning the guy shooting pool gives a CD to Richard Gere, he says that the song they were listening to is the fourth song when in fact it's the first song on the album.
Factual error: Though the movie is set in Chicago, Laura Linney refers to the prosecutor's office she works for as the DA's office. There is no DA's office in Chicago. In Chicago, this office is called the State's Attorney's Office.
Answer: They knew he was a street kid and looked where the homeless and beggars hang out (under a bridge) they recognised him by his bandaged ear, from where the crucifix earring was ripped.