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.

The New York police officer killed in a mass shooting in a Manhattan skyscraper on Monday was an immigrant who left behind a pregnant wife, two young sons and distraught parents, while friends and officials in Bangladesh and the United States described him as a hero.

Police have lined up four rows deep to pay respects to a fellow officer who was among the victims of a gunman's rampage at a Manhattan office tower.