Investigators are trying to determine why an armed veteran opened fire in a federal building in Manhattan, fatally shooting a security guard before killing himself.

Federal agents swarmed the New Jersey home of Kevin Downing late Friday. They say he carried out the shooting earlier that evening.

Investigators say they were hoping to find notes offering a possible motive.

They say the 68-year-old former federal employee and armed forces veteran slipped through a side door and fatally shot the guard before turning the gun on himself.

Downing previously worked for the Bureau of Labor Statistics.

The company that employed senior guard Idrissa Camara says he had been scheduled to leave work at 4 p.m. but agreed to stay for an extra shift.