Well, from the mugshot, there does appear to be a minor contusion on Boucher's lower lip, but his apparent lack of injury relative to Rand Paul's is consistent with an abush attack of some kind.

The puzzler is that Boucher does not seem to have a prior history of violent behavior - not that it would be unheard of for someone with a clean criminal record to one fine morning decide to hurt someone.  And we can't rule out a psychiatric issue, or the effect of drugs, or even an organic brain disease.  I'm reminded of the slaying that occurred at the old McDonald's restaurant near University Avenue, where one morning a random seated customer had his head bashed in from behind by someone with mental health issues wielding a heavy hammer.  Until that moment, his killer didn't have a remarkable criminal history either.