New York City is mourning NYPD Officer Didarul Islam and three other people killed in Monday's shooting inside an office building at 345 Park Ave.

Family, friends, and colleagues of slain NYPD officer Didarul Islam gathered at Parkchester Jame Masjid Mosque in the Bronx for his funeral.

A New York City police officer who was among the four people shot and killed by a gunman during a rampage at a Manhattan office tower will be laid to rest Thursday. Officer Didarul Islam, 36, was fatally shot Monday in a midtown building housing the National Football League’s headquarters.

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.

NFL commissioner Roger Goodell called Monday’s shooting in New York City an “attack on humanity” ahead of Thursday night’s annual Hall of Fame game in Canton, Ohio.

The NFL season kicked off at the annual Hall of Fame game with a moment of silence for the four people killed earlier this week by a shooter who was targeting league headquarters in New York