Thomas Matthew Crooks Called Solitary, Highly Intelligent Years Before Shooting

The world is learning more about Thomas Matthew Crooks -- and we've got additional insight from his former peers and even a teacher, who says he was smart ... but notably solitary. TMZ spoke with a couple of Crooks' ex-classmates from Bethel Park High School -- who were in his graduating class -- and both of them, who asked not to have their names released, tell us they knew him as a loner, but not one prone to…