How law enforcement use social media for forensic investigation

From Mashable:

Forensic analysis of social data is performed post-incident. Naturally, investigators will gravitate to where the evidence exists — in this case, sites such as Facebook, Twitter, Flickr, YouTube and others. Although the photo and video evidence is sometimes posted by the criminals themselves, investigators can also utilize information posted by others to both strengthen a case and even identify the perpetrator of a crime.

As always, the rest of the article is at the link above.