Yeah, this has most of the hallmarks of a textbook self-inflicted hate crime as a plea for attention.
* Crazy crime/vandalism that sounds more like something from a movie than acts you typically read on the police blotter? Check.
* Committed in an area where the victim group is much more prevalent than their supposed “haters”? Check.
* Victim is in a position to materially benefit in some way from the sympathy and attention following the incident? Check.
The only thing missing is the poorly mispelled epithet, or the incendiary logo drawn improperly. However, using “liberal” as a hate epithet is similarly a giveaway that the perpetrator is not really a conservative. A conservative, in anger, might call someone a socialist, a commie, a traitor, etc, but would consider the label “liberal” as being pretty mild. Someone who would hate lefties enough to kill a cat to send a message like this would certainly come up with a more insulting term to use than liberal. The most reasonable conclusion is that the word was inscribed instead by someone who considers themselves a liberal and is looking to drum up sympathy.
Perhaps they wrote “Liberal” because “Progressive” wouldn’t fit.