The man was armed with a shotgun and a pistol when he arrived at the Knight Transportation office in Katy, about 20 miles west of Houston, according to Harris County Sheriff Ron Hickman. The sheriff said the man "parked right outside the building and came straight in."
PHOTOS: Katy-area workplace shooting
The man was heard by workers saying something to the effect of "you all ruined my life" as he walked through the building, and may have been looking for someone, sheriff's spokesman Ralph Gonzales said.
The gunman fatally shot one man, who was found dead at the scene by responding officers. Two other workers were injured by shrapnel or other debris from the gunfire, and both were treated at the scene, Gonzales said.
The gunman's identity has not been released, but the murdered supervisor is Michael Dawid. Relatives say he leaves behind a wife and toddler.
"He's that good of a guy. I don't have any words, that good of a guy. You know I'm going to miss him," said Tomas Faz, Mike Dawid's brother-in-law.
Faz said when the family heard about the shooting at Knight Transportation, they were in shock.
"It's a good office. It's quiet. You would never hear things like that," said Faz.
Dawid was a supervisor at Knight Transportation, when Faz said he was killed.
Faz said Dawid has a two-year-old son, Noah. He leaves behind a large family and will be missed by many.
"He's in heaven. He's with God. He's in God's hand's now. He can watch over Noah, his son," said Faz.
We've learned the gunman was fired a few weeks ago from the business, and recently paychecks stopped coming.
The company is near Katy ISD's Morton Ranch High School. School officials say the school was on lockdown as a precaution. A deputy injured his knee during the lockdown process.
VIDEO: SkyEye flies over Morton Ranch High School
Hickman had no information on how long the man had been employed by Knight Transportation, which provides truckload transportation services.
The Phoenix-based company released a statement Wednesday saying work at the facility was being suspended until the investigation was complete. It said counselors would be on site to support employees.
The company confirmed an employee was killed during the shooting, saying: "Our deepest sympathies are with the family during this difficult time."
"This was the action of a lone former employee," the company added. "Knight is doing everything possible to ensure the safety of all of its employees."
The Associated Press contributed to this report.