Nothing conclusive was ever proven about Whitman’s tumor having an effect on his behavior. Months before his rampage, he told a psychiatrist he was thinking about going up in the Tower and shooting a bunch of people - but the shrink didn’t take it seriously enough, notify law enforcement or anything.
Of course, that was a different time...
Whitman left a note asking that an autopsy be performed to see if something was wrong. I guess he knew he would not live through the whole thing.
I took a criminology course and our textbook had a whole chapter devoted to the Texas Tower shootings. It said they found a tumor but that it could not have caused his behavior.
I don’t know a thing about medicine or psychology but I do believe the tumor was what caused his actions.