CNN —  

A former employee opened fire Wednesday at a transportation center in Texas, killing one person before turning the gun on himself, the sheriff said.

The gunman had been terminated from his job at Knight Transportation in Katy, Texas, earlier Wednesday morning, Harris County Sheriff Ron Hickman told reporters.

He later returned to the business, this time armed with two guns, the sheriff said.

“He parked right outside the building and came straight in,” Hickman said.

Authorities haven’t identified the victim or the gunman, who also died. Investigators believe the shooting was a “retaliatory act,” Hickman said, and they assume the person killed was a supervisor.

Another employee at the center was injured and treated at the scene, Hickman said, and a sheriff’s deputy who responded to the shooting was hospitalized with a knee injury.

The shooter entered the building with two weapons: a shotgun and a pistol. Only the shotgun was used in the shooting, Hickman said.

Nearby schools went on lockdown after the shooting, CNN affiliate KPRC-TV in Houston reported. Officials later tweeted that the lockdown had been lifted and all students and staff were safe.