A lot would depend on where the head wound was located and whether the weapon was found near the body but, yes, my first guess would be suicide because:
a) a judge would be the type of person who could hide a gun in their briefcase and not have it checked and
b) this happened in the judge's chambers where one would presume only certain people have access.
So, if it were NOT a suicide or an accident (cleaning his gun) then you'd have to conclude a murderer would need to get a gun past security and have access to the judge's chamber making for a rather small list of available suspects. Not impossible that it's a murder but more improbable. Again, the head wound and the presence of a weapon at the man's feet will tell a lot.