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By Jacquellena Carrero and Corky Siemaszko

A fired Texas trucking company worker bent on revenge returned to the office Wednesday and fatally shot a supervisor with a shotgun before he killed himself.

"You ruined my life," the worker yelled as he opened fire, Ryan Sullivan, a spokesman for the Harris County Sheriff's Department, told NBC News.

That blast killed the supervisor and wounded two other workers at Knight Transportation in the Houston suburb of Katy, Sheriff Ron Hickman said earlier. Then the disgruntled worker turned the weapon on himself.

Police respond at the scene of shootings at Knight Transportation in Katy, Texas.Phil Archer / KPRC

"Other than he was terminated, we don't know anything about him," Hickman said. "He parked right outside the building and came right in."

Hickman said the man had been fired several weeks earlier and called the shooting a "retaliatory act."

"The weapons involved was a shotgun and a pistol, but only the shotgun was used," the sheriff said.

Hickman did not release the names of the dead men or the wounded workers, who were struck by debris.

Also, a deputy responding to the shooting suffered a knee injury and was taken to the hospital, the sheriff said.

A Knight Transportation official said this was the act "of a lone former employee" and that the Katy facility will be closed "pending completion of the investigation." The official also did not identify any of the workers involved in the deadly confrontation.

Meanwhile, the lockdown that had been put in place after the gunfire erupted around 8:30 a.m. was lifted at the nearby Franz Elementary School and the Morton Ranch High School.

Knight Transportation is an Arizona-based trucking company with locations around the country.

On its website, the company says it has a "fleet of over 4,000 tractors and more than 8,800 trailers" and employs nearly 5,000 "associates."

This is a developing story. Please refresh for updates.