BOSTON (AP) — The degenerative brain disease that has besieged the National Football League for two decades with a billion-dollar lawsuit, congressional hearings, an A-list movie and an unrelenting cortege of ex-players’ obituaries has now intruded on America's favorite sport in the most violent manner yet. The Las Vegas casino worker who killed four people in a New York City skyscraper that is home to the NFL's headquarters carried a note blaming the league for mental health problems he attributed to his time as a high school football player. Shane Tamura, 27, said in a three-page note found in his wallet that he had chronic traumatic encephalopathy — diagnosable only after death — and implored those who found him: “Study my brain.” Among his grievances against the NFL was a claim that the league put its profits ahead of player safety by concealing the harm CTE, and football, can cause.