[quote=Zane620]
Hey thats what a cop pretty much did XD
[/quote]

It's revealed why he did in P4A, or rather, was more specific. Kurosawa was caught during the Dark Hour, as in he didn't turn into a coffin like his colleagues, and was saved by Mitsuru. Among the police force, he knew no one would believe him, so he began working secretly with the Kirijo group and helping them.