Mourners gathered in Manhattan’s Bryant Park Tuesday evening to honor the four people killed in a shooting in a Midtown skyscraper, as investigators work to understand exactly how and why the shooter carried out the attack.

Five people—including the suspected perpetrator Devon Tamura and NYPD officer Didarul Islam—were left dead at an office building in Midtow.

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