From the management side of things, there’s only so much we actually can do. This is one of the reasons we don’t allow questions that ask for help with illegal activities, aside from the obvious “We don’t want to help criminals” part. IP addresses are not an exact science. For instance, it may be a public location like a school, library or even an apartment building (a public IP was used in a recent example), or an AOL IP address (which are shared by a huge amount of people), or a proxy used to conceal the real location. Email addresses are similarly only somewhat useful. People use ‘throw-away’ addresses to join sites all the time, some of which are designed to conceal their real identities. (Note: mods can’t see email addresses, but I can.)
Then there’s the whole thing about knowing what is real and what is fantasy. It’s pretty darn difficult to tell between the two, sometimes. For all of these reasons, a theoretical crime that has already been committed is generally not something we’d pursue, beyond removing the question and/or advising the individual to turn themselves in.
All of that said, if I believed anyone’s life was in imminent danger, I would try my very best to prevent the crime. Provided that the IP is not a proxy, it can be used to determine a general location. From there I would contact the local authorities with whatever information I had available.