HAUPPAUGE, N.Y. -- An investigation is underway into what caused a garbage truck to lose control and end up in a deadly crash in Suffolk County.

One person was killed and two others were injured.

Police say the truck rear-ended a school bus and three cars at a red light at around 9 a.m. on Monday on the Long Island Expressway service road near Motor Parkway in Hauppauge.

Witnesses described a chaotic chain of events.

"You can see the truck didn't even stop. It just kept pushing the cars out of the way," witness Preet Singh said. "It was like a big blast, when the truck hit the cars. It was like a boom sound."

The Department of Sanitation said it was one of its new trucks, but it was operated by a private vendor.

No one on board the bus was hurt.