EMCO’s UnLock IT is a cool freeware application for Windows that allows you to gather more details/information about who is locking a file. Once you enter the path of the locked file, the software will display the following information:

1) The process that has locked the file
2) Process ID
3) Process path
4) Owner of the process and its SID

You can choose to integrate the application as a context menu in Windows Explorer

Download here