Since not even the police and the FBI know when he was radicalized, I’m not sure how you would know. The only way you could presume to know this is if you’re psychic, or if you heard that he was brainwashed before entering the country because you’re taking as Gospel some of the things other people have been saying as part of an insidious political agenda to justify barring people from entering the country.
I can only hope that OSU teaches its students to cultivate the ability to avoid what this post is guilty of: the conflating of facts with rumors and the inability to distinguish an actual news story from the inflammatory rantings of a propaganda-peddler on Twitter.