Hi Carroll,
Thanks for the feedback. While we don't have the ability to see who changed an individual use case or requirement (which I agree would be nice), since you are using a shared project, you should have access to this information already, via the version control system. Please try right clicking on a package in the project browser and selecting View History. This will bring up a dialog that shows each time the file was checked in, along with who checked it in and the comment, if any, that was included when it was checked in. Does this get you the information you're looking for?
Regards,
Doug