Someone left the organisation but before leaving, he locked all the files for an unknown reason.
How do you unlock them all so that the other developers can work?
For the following operation, you will need to be either a project administrator for the project you want to undo the check-in on or a Team Foundation Administrator if you want to do this across all projects.
If you still have the username of the person, you can simply do something like this:
tf lock /lock:none /workspace:WorkspaceName;USERNAME /recursive $/
To get the list of workspaces for a user, just run the following command from the same prompt:
tf workspaces /owner:username
For more commands, check tf /?