User account with admin rights

Hello:

I have a user account with admin rights assigned to it. In the wee hours of the night, someone tried to logon with this account and locked it. When I went to unlock the account, I looked at the “Last Intruder Address” — which listed nothing. Usually it lists a segment number and a MAC address but this time nothing. I went back in the log about a week and it listed this: 81782022:000000000001
How can I find out who this is? Is there additional logging I can turn on the track down the individual? Thank you!