The man who shot and killed four people in Manhattan had legally purchased a firearm in Nevada, where he lived, despite a record of mental health problems.

The Manhattan high-rise shooter, a former high school football player, left a note referencing the brain disease CTE and appeared to have targeted the NFL’s offices, authorities said.

A gunman who killed four people inside a Manhattan office tower blamed his mental health problems on the National Football League and intended to target its headquarters but took the wrong elevator, officials said Tuesday.