I’d be on the guy or group that converted him like flies to honey..they go after the unstable because they know they can manipulate them....find out who converted him and you can bet someone can get nailed and stopped.
He (the terrorist) may have been introduced to someone through his training for competition. They may have said, study these Koran verses, and dedicate yourself to Allah if he will help you win the next Championship. A Faustian Pact is reached, in a moment of competitive, superstitious zeal. Lo and behold, he does win the next Championship. The next day, the “training assistant” reconnects, all ready to collect the young man’s soul.