MIKE was killed and he was killed by JEFF
1) to establish who was killed;
- Dan ran in the NY City marathon yesterday ( So he was not the one who was killed)
- Jeff is a topnotch computer consultant and wants to install Ben's new computer next week. (So JEFF and BEN are not the ones killed)
- Jack has been in seclusion since the crime; The murderer is Jack's brother. ( So JACK is not the one killed)
THEREFORE - MIKE was the one killed
2)
- The murderer had his leg amputated last month. + Dan ran in the NY City marathon yesterday ( means DAN is not the killer)
- The murderer is Jack's brother. + Ben met Jack for the first time six months ago (means BEN is not the killer)
- The murderer is Jack's brother. (means JACK is not the killer)
CONCLUSION :
MIKE was kiiled and DAN,BEN and JACK are innocent.
THEREFORE - the killer is JEFF