The Nevada man behind a shooting spree in a Midtown Manhattan office building may have originally been targeting for the NFL headquarters, sources say. Police sources told ABC News Tuesday that a page of the note found in suspect Shane Tamura's pocket alleged the National Football League had concealed the dangers football contact could cause to players' brains to maximize earnings.

Terrifying scenes in Midtown Manhattan showed office workers running for their lives with their hands in the air. The surveillance image shows the suspect, identified as 27-year-old Shane Tamura, entering the skyscraper with an M-4 assault rifle at his side.