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.

The horrific mass shooting at a Midtown office building on Monday was the deadliest gun attack in the Big Apple in 25 years. Shane Tamura gunned down four innocent people — including an NYPD cop and a business executive — before turning the gun on himself late Monday.