Hard Drive Forensics Question

I'm trying to answer a question for a customer regarding historical file copying on his personal Mac computer. I'm not sure if this is the right list to post this to; please redirect me if I should be asking this elsewhere.

Equipment Details:
Powerbook G4 with a 75 GB hard drive - purchased 3 or 4 years ago.
Samsung Pleomax USB power drive.

His former employer believes that documents on this external device might have been copied to his personal Powerbook. They are demanding that he allow them to have the drive imaged so that they can determine prove whether he did or did not copy these files to his home computer.

The weekend before he left his former employer he opened several documents on this external device using MS Office and maneuvered others using Finder. According to my customer all files opened were on USB drive and then saved back to it.

He left the company six months ago. When he left his former employer six months ago he returned the Pleomax drive to them.

My opinion is that looking at an image of his personal computer's hard drive will not prove conclusively whether or not he saved files from the company's Pleomax to his personal computer. Can someone either validate that or indicate why the image would provide that information?

He is prepared to allow his personal computer's hard drive to be imaged. I am concerned that doing so will breach his own privacy since he stores personal finance, correspondence, etc. on it.

Thanks so much.