HOUSTON, Sept. 2 (Xinhua) -- The Police Department of Odessa, U.S. state of Texas, said Monday afternoon that the gunman in Midland-Odessa mass shooting was fired over the weekend from an oil field services company and called 911 before the shooting spree.

Police Department of Odessa told a press conference held Monday afternoon in the University of Texas of the Permian Basin (UTPB), about 7 km northeast of Odessa, that the suspect Seth Aaron Ator, 36, and the oil field services company called 911 after Ator was fired on Saturday.

Ator left by the time police showed up. About 15 minutes later, Ator was stopped by a Texas state trooper on an interstate for failing to signal a lane change. When the trooper pulled over the car, he was shot by the gunman.

The vehicle continued westbound into the city of Odessa, and the driver shot random individuals.

The suspect then ditched the vehicle he was using and stole a mail truck and there were more victims after that.

The shooter was encountered by and exchanged fire with law enforcement officers including those from Odessa, Midland police and TxDPS near a local movie theater named Cinergy, and was killed at that location.

Texas Governor Greg Abbott tweeted on Monday that "not only did the Odessa gunman have a criminal history......he also previously failed a gun purchase background check in Texas......& he didn't go thru a background check for the gun he used in Odessa. We must keep guns out of criminals' hands."

The governor attended Sunday's press conference, also held at the UTPB. He said, "I have been to too many of these events." He named several shootings that have occurred during his term, including the Dallas shootings that killed police officers, then Sutherland Springs, then Santa Fe High School, then El Paso and now Odessa and Midland.

The Saturday shooting was less than a month from another deadly mass shooting in Texas that shocked the whole nation and the international community. On Aug. 3, a 21-year-old gunman opened fire at a Walmart store in El Paso, killing 22 people and injuring at least two dozen.

"I am heartbroken by the crying of the people in the state of Texas. I am tired of the dying of the people of Texas. Too many Texans are in mourning. Too many Texans have lost their lives. The status quo in Texas is unacceptable, and action is needed," the governor said.

Located in West Texas, the Midland-Odessa is a metropolitan area with a population of around 240,000. The economy of the area is heavily dependent on the petroleum industry.

Odessa is a city in western Texas, about 30 km southwest of Midland. Located in the Permian Basin, it is an oil industry center.