Has the killer said why he did it yet, I can't find info on such?
The suspect said he bore a grudge against a "specific organisation" and believed Mr Abe was part of it, and that his grudge was not about politics, the police said, adding it was not clear if the unnamed organisation actually existed.
Several Japanese media outlets described the organisation as a religious group.
(Source).
Sounds like the assassin is a bit of a loose unit.