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.

Police lined the streets of New York City to pay their respects to fellow officer Didarul Islam, who was among the four victims of a gunman’s rampage Monday at a Manhattan office tower.

There were 23 shell casings and 13 bullet fragments recovered from the lobby of 345 Park Avenue and 24 spent shell casings on the 33rd floor, police said.