Police say a gunman who killed four people in a Manhattan skyscraper before taking his own life claimed to have a brain disease linked to contact sports and was trying to target the National Football

Shane Tamura, the 27-year-old shooter who fatally shot himself, was a former standout high school football player who claimed he suffered from CTE, the brain disease that has been found to be common in football. Chronic Traumatic Encephalopathy is a degenerative brain disease that occurs with repeated head injuries.