Four people were killed, including an NYPD officer, and a fifth person was injured in a mass shooting at a Manhattan office building on Monday. Police say the suspect had a history of mental illness. --- Subscribe to ABC News on YouTube: https://abcnews.visitlink.me/59aJ1G ABC News is your daily source of breaking national and world news, exclusive interviews and 24/7 live streaming coverage. Download the ABC News app for the latest headlines and alerts: https://abcnews.go.com/devices Watch 24/