A shooting rampage at a St. Louis, Mo., manufacturing plant killed at least three people and injured five others, Thursday.

Police say the shooter, 51-year-old Timothy Hendron, was a long time employee of the ABB Group's plant.

According to investigators, Hendron began shooting in the parking lot around 6:30 a.m., then later moved into a nearby building. He was armed with an assault rifle and handgun.

Police spent several hours after the shooting searching for him. Unconfirmed reports said he was found dead inside the building.

In 2006, Hendron sued the company over retirement losses. The lawsuit went to trial Tuesday.