There are criminal statutes, but the law needs to show intent and the person who committed this crime is claiming it was an "accident" Hardly an accident to reformat a hard drive and reinstall the operating system.
Hmmmm....
Have you tried pounding sand?
So you had valuable data that you didn't back up, you didn't password protect your boot, and you didn't have physical security for the machine? At least they were nice enough to re-install the operating system for you.
Have you tried a data recovery service?