In the Moderator Control Panel, the reports show the IP address of the reported message (both private or public message), but not the IP address of the reporter (see screenshot)

It would be useful to have that address, especially if guests can report a message (not enabled by default but possible with phpBB permission system) or if someone steals an user password and then reports (private) message. Alternatively, you can list reporting events in a log (such as moderators log, the only one readable by moderators ; the bumping, deleting & locking events by users are recorded here).