New York City detectives investigating this week's mass shooting were interviewing the attacker's associates in his home state of Nevada on Wednesday, as gun safety advocates expressed dismay that he was able to buy a gun there legally last month despite two reported mental health hospitalizations.

The shooter behind a deadly rampage inside an office building in Midtown Manhattan on Monday evening was apparently targeting NFL offices there, New York City Mayor Eric Adams said Tuesday morning.Law enforcement sources say investigators recovered a three-page rambling note from gunman Shane Tamura's wallet in which he referenced the brain disease CTE.

" The mayor confirmed the shooter had played high school football, not at the college or professional level. Security camera footage showed the gunman's methodical approach, Adams said. "When you look at the

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.

No motive has been announced. A suicide note was found expressing grievances with the NFL and saying Tamura suffered from CTE, a source said. Follow for live updates.

Live updates and developments about a shooting in New York City's Midtown. Five people, including the gunman and a police officer, are dead.