As today's show begins we learn of a possible motive in the murder of four people in a midtown Manhattan mass shooting. The gunman, identified as 27-year-old Shane Tamura of Las Vegas, walked into a Park Avenue high-rise with an assault-style rifle and opened fire. That building is home to the corporate offices of the National Football League. A source tells CNN a suicide note was found on Tamura's body, and the shooter wrote he was suffering from CTE, a brain disease linked to head trauma, which can be caused by contact sports.