Four people were killed and a fifth was injured in a mass shooting at a Midtown Manhattan office building on Monday.

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.

Blackstone, one of the world’s largest investment firms, confirmed one of its employees, Wesley LePatner, was among those killed. A Yale graduate, LePatner was a real estate executive, according to Blackstone’s website, and spent more than a decade at Goldman Sachs before joining the firm in 2014.