My boss's files suddenly dissapeared , one of the IT staff ( untrusted person ) said that he recovered his files using " recover my files" software.He did that very quickly that I'm suspecting that he used that software from the begining, how can I make sure that the software is the one that restored the files. and that he is not the one who deleted the files from the begining??

Without getting into your office politics, let me suggest a free program that will recover files that have been ‘recently’ deleted. Run it as soon as it is noticed that a file has been deleted. Download the free Recuva program from here http://www.filehippo.com/download_recuva/

If you know, where files got lost (deleted) on the disk, and they have not been overwritten yet, every IT affine person with the proper tool can recover these files quickly. Best greetings from Germany Olaf