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.

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

Officials said the gunman fatally shot himself after his attack, which set off a chaotic scene that rippled out into the heart of Manhattan during rush hour.