It's become a common practice for police look into the online activities of people they are investigating, but when authorities come calling to the people who have that info, what exactly do they find out?
The Boston Phoenix has a lengthy cover story on the murder investigation of "Craigslist Killer' Philip Markoff, which is worth a read for its own sake, but also includes some interesting side information about what happens when police ask a social network to give up what it has on you. In order to catch Markoff — who was accused of murdering Julissa Brisman, and robbing two other women after hiring them for erotic services on Craigslist — police gathered a massive amount of digital evidence, tracking his online movements via email, message board postings, and his social media accounts.
As part of their story, The Phoenix obtained numerous police files via a Freedom of Information Act request and discovered that the caselog included a subpoena issued to Facebook for Markoff's profile information and Facebook's response. In addition to the technical information like login and IP data, Facebook provided Boston police with text printouts of Markoff's wall posts (both his wall and any conversations he had on other users' walls), as well as paper copies of the photos he posted and photos posted by other people that he was tagged in. It was basically a full accounting of all of Markoff's activity on the site.