Police have warned internet users to be careful over the amount of information they reveal online.
Following the murder of British student Matthew Pyke by German office worker David Heiss, detective chief inspector Tony Heydon of Nottinghamshire Police claimed that Heiss was a keen internet and online gaming user and became obsessed with Pyke's girlfriend Joanna Witton.
Heydon told BBC News: “David Heiss was very clever on the internet, and he learned a lot of information about Joanna Witton and Matthew Pyke and others. It is very, very interesting that he could do that.
“One of the things that's important here is that people need to realise that on their computers there is a lot of personal information that other people can gather. We know that Heiss found out a lot of information about where they lived and where they worked and all sorts of things about their social network that perhaps now with hindsight they wouldn't want him to know.
"So people need to bear that in mind when they are on their own systems using Facebook, people need to be careful."