"format the computers"
please create a P to V before you scrub the computers
to just format them is a huge mistake
you are literally destroying evidence .
This!! +1
Go get a brand new computer to follow through with all your tracking efforts. Pull your old stuff offline, unplug and access needed info later. Based on your actions thus far, I would hire someone to help you out.
Truly sux man, but you need help to understand better how to catch this thief and prevent it from happening in the future.