During evening rush hour in New York City on Monday, a man calmly walked into a Park Avenue office building lobby and killed a police officer, then opened fire on other innocent strangers.

A gunman opened fire inside a Midtown Manhattan skyscraper on Monday, killing four people, including an off-duty NYPD officer, according to authorities. A video showed terrified people running from the office building at 345 Park Ave.

F amily, friends and members of the New York City Police Department will come together on Thursday for a funeral for the "hero" officer who was one of four people killed in the Midtown Manhattan mass shooting.