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.
Active shooter situation in Katy. @abc13houston #breaking pic.twitter.com/axMOr7uSJb
— Charles Fisher (@NewsCameraFish) May 4, 2016
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.
#BREAKING: HCSO responding to reports of shots fired @ 20400 of Frans Rd. HROU & Mobile Command Units are enroute to the location #HouNews
— HCSOTexas (@HCSOTexas) May 4, 2016
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.
"Y'ALL RUINED MY LIFE," shooter said before shooting supervisor, then himself. That's what @HCSOTexas says workers told investigators #abc13
— Courtney Fischer (@CourtneyABC13) May 4, 2016
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.
Active shooter situation at Knight Transportation on Franz Rd in Katy. @abc13houston pic.twitter.com/0GVSPwobMi
— Charles Fisher (@NewsCameraFish) May 4, 2016
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.