user registration in custom event

Hello there,

I'm developing an application where in the custom event is used to store extra info about the event itself and is necessary to save also the user that add this information.
other than manually ask to type the ID of the operator could be possibile to save automatically this information?
the application is for security survelliance and the custom event is used to store the extra information about the event, so at this time storing also the user that register the info, and close the event is really important.
this could also be used in generating the report so the log book is much more detailed.

thanks
ezio