Hello Robert,
If you already created the access control policy based on the users and if you can see the initiate user data in the connection events then you can create the reports based on the same.
Here is the quick reference on how to create report based on users:-
http://www.cisco.com/c/en/us/td/docs/security/firesight/541/user-guide/FireSIGHT-System-UserGuide-v5401/Reports.html
PFA sample screenshot.
Rate if this answer helps you.
Regards
Jetsy