File folder security question - windows server 2008

I'm the admin of a windows 2008 server. 

I noticed (in the folder security tab) that a user had access to certain folders on our server that he should not have had access to. I have no idea how he got that access. 

Is there any way to see when he was granted access to those folders and who gave it to him? Or any other information on how this could have occurred. 

Also is there a way to see if that user have viewed or done anything with the files in the folder?

Thanks in advance.