. >> owen thomas to me was a critical case.a 21-year-old who was a hard-hitting lineman from the age of nine on. >> and then, seemingly out of nowhere, he decided to take his own life. never been diagnosed with a concussion, never had a problem in the world. >> narrator: owen thomas had hanged himself in his off-campus apartment. chris nowinski secured his brain for dr. mckee. without any history of diagnosed concussions, it seemed unlikely he had cte. >> i was fully prepared to see nothing. i remember late at night looking at the brain and thinking, "just going to knock this one off." and it just floored me. i just couldn't believe what i was seeing. >> narrator: such an advanced case of cte had never been found in such a young person. >> in, like, 20 spots in his frontal lobe. he's 21. he's so young. that changes the game to me. >> wrapped up and brought down by owen thomas. >> narrator: because he'd never had a diagnosed concussion, dr. mckee suspected thomas might have gotten cte from the everyday sub-concussive hits that a