A gunman who killed four people at a Manhattan office building before killing himself claimed in a note to have a brain disease linked to contact sports and was trying to target the National Football League’s headquarters but took the wrong elevator,

A fifth shooting victim -- an NFL employee, according to Commissioner Roger Goodell -- was injured and taken to the hospital in critical condition, officials said. That victim was listed in stable condition on Tuesday morning, according to a source familiar with the individual's status.

Mayor Eric Adams told MSNBC the gunman referenced CTE, a disease linked to head trauma, in a note before killing four people at 345 Park Ave., which houses the NFL.