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.

Investigators believe the gunman in a deadly New York City shooting was targeting the NFL headquarters, as he entered the building where the offices are located. A note on his body claimed he had CTE from football.