1. Where did he first encounter the propaganda?
2. Where did that online activity then migrate?
4. Was he in contact with any militia groups, who offered weapons training?
5. Did he have a weapons fetish?
6. WHO did he interact with online?
Please do not shame them.
Encourage them to come forward. They can reveal the patterns of behavior that other parents need to know.
In the few bits of data we do have, it seems radicalization is increasing in speed.