“We didn’t talk but he never said anything about this” sounds really stupid of the brother.
I hope that we learn answers to such questions (about the alleged perp) as these:
— what were his previous political associations?
— is there any actual contact with religious zealots?
— what is the role of drugs in producing his mental state?
— did he have any prior diagnosis of mental illness and was he under any form of treatment either recently or in the past few years?
— who knew in advance of his potential to carry out this act?
— are there any reasonable grounds to suspect that the alleged perp is a patsy set up by others for whatever reasons?
Until we know any of the above, we basically know very little about this action.