[Re: Why did Gamzee go on a killing spree.] It was later in the comic that we didn't find out why until a lot of the comic that Dirk had been 'influenced' by Lil Cal through Caliborn. Gamzee had the same exposure to Lil Cal as Dirk but not the willpower to resist Caliborn's influence.

Dirk’s Cal was empty so he couldn’t have been influenced by it.  Bro possibly was tho, and he was p. awful.