(Reuters) - A man who had been fired from a Houston-area trucking firm on Wednesday returned to the company and fatally shot a co-worker with a shotgun before taking his own life, the Harris County sheriff said.

The gunman was heard shouting “y’all ruined my life” before he started shooting, the sheriff’s office said, adding he walked past at least person in the office before he opened fire.

Sheriff Ron Hickman told reporters at the scene of the shooting at Knight Transportation, that the co-worker who was killed appeared to be a supervisor. He did not release the names of those killed.

“The suspect is believed to have taken his own life after being terminated early this morning,” the sheriff’s office said on its Twitter feed. It added that the suspect, armed with a shotgun and a pistol, fired at multiple employees.

“Only the shotgun was used,” Hickman said, adding that the shooting was “a retaliatory act.”

One other person was injured in the incident after being hit in the face with what appeared to be a “projectile,” possibly a shotgun shell, Hickman said.

“This was the action of a lone former employee, who also died as a result of today’s events,” the company said in a statement, offering its sympathies to the family of the employee shot by the gunman.

“One other employee was confirmed to have injuries, and was treated at the scene and released,” the Arizona-based company said.

Dozens of patrol cars, a SWAT team, as well as several ambulances were dispatched to the business located in Katy, about 30 miles west of Houston. A nearby school was temporarily locked down.