Jeff Killed Mike

1. Jack is not the murderer, because he is the brother of the murderer.
2. Dan can't be the murderer since he ran a marathon, and the murderer recently had his leg
amputated, and wouldn't be running a marathon of any magnitude that quickly.
3. Ben is not the murderer if he just met Jack, since Jack and the murderer grew up together.
4. This leaves Jeff and Mike.

Since Jeff is still alive (he wants to install a new computer next week, present tense) he must be
the murderer. Mike also didn't grow up with Jack. It has been determined that Jack, Dan and Jeff
are all alive. Ben must also be alive since Jeff plans to install Ben's computer next week. This
means that Jeff killed Mike.