He allegedly told someone his briefcase was stolen. I suppose a really angry neighbor might want to snatch a briefcase if he thought there was something in it that would work against him in in a lawsuit over the property dispute.
But then recall that O'Neil guy with the FBI who left his briefcase unattended or misplaced his briefcase in Tampa? Supposedly the thing contained info relating to aircraft security. He was transferred to the NY FBI office and ended up getting reported as killed in the 9/11 attacks on the World Trade Center.
John O'Neil left the FBI and took the head of security job at the WTC, I believe. He was killed on 9/11/2001.