Once a promising athlete, the 27-year-old faded from public view—until he showed up at 345 Park Avenue, gun in hand.

In a video message, Tisch said Tamura left a suicide note and claimed to be suffering from chronic traumatic encephalopathy (CTE), possibly from playing high school football. Tamura also blamed the NFL and asked that his brain be studied for signs of the degenerative disease.

The gunman suspected of targeting the National Football League headquarters In New York, killing four, was a former standout football player at two Southern California high schools.