Crown Law contacted the US Government on the police's behalf. US authorities then went to court and had a warrant issued against Facebook, which released the information. "That's quite a long process," Mr Thornton said. "We got that back just before Christmas."

In addition, the FBI assisted in testing forensic evidence in the murder case.

The FBI and the Australian Federal Police had tested hundreds of forensic samples from the case, along with local agencies. Evidence examined by the FBI included a foot imprint found in dust at the murder scene.

Last July, Reuters had this report on the Feds' use of Facebook.

Where does it stop? With a suspect or person of interest's friends, or does it extend to friends of friends and members of the same Facebook group? How about people who have posted on your wall, tagged you in a photo or invited you to an event? Considering how many people use Facebook for professional purposes and have oodles of friends they've never personally met, it seems like there should be strict limits as to what courts can order Facebook can provide to law enforcement pursuant to its one-sided, secret requests.