At some point in the past I had the surreal experience of opening a news website and seeing a familiar face on the front page. Not a celebrity, rather a man whose face had been in some small subfolder of my brain for several years.
The man had been convicted of serial rape. He would drug victims and record them. He was known to be active within a certain time range from the timestamps of the videos. He repeated this dozens of times and was only caught after the final victim woke up during the act. Authorities appealed for people to come forward with any more information because they believed there could be more victims than were discovered from the videos.
By cross-referencing the location data from my phone with the date of an event my Last FM profile and the location of his home, I was able to confirm why he looked familiar. This allowed me to contact the authorities and bring the start of the known time frame significantly forward.
(there might be enough information in this post for the perpetrator to be identified - if you do, please keep it to yourself)