Track user file activity

Hi

I work at a small design company. We all (12 members of staff) run macs and store most of our files on a xserver currently running OS 10.7 using unique user names and passwords.

Unfortunately we have had to suspend a member of staff and I would like to be able see if, before leaving, they took any company files.

How could I do this? I also have their laptop, which was confiscated before leaving.

Any help would be greatly appreciated