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.

New York City has some of the toughest gun laws in the nation. But Monday’s mass shooting showed their limits, security experts said.

The gunman accused of killing four people in a Midtown Manhattan office tower bought the AR-15-style rifle used in the attack from his boss at a Las Vegas casino.

Photos released by the New York City Police Department show the assault-style rifle 27-year-old Shane Devon Tamura used to fatally shoot four people – including a police officer – and wound one before killing himself in Midtown Manhattan.

New York City Mayor Eric Adams and officials share updates on the shooting in Midtown Manhattan.