*Correction appended

Texas Gov. Greg Abbott tweeted Monday that the gunman in Saturday's mass shooting in Midland and Odessa had previously failed a gun purchase background check and did not go through a background check to buy the gun used in Saturday's incident.

Abbott's tweet did not say why the 36-year-old Odessa man didn't pass the background check or how he obtained the rifle he used to kill seven people and injure 22 others — including a state trooper and two police officers. The gunman died after a shootout with police outside a Midland movie theater.

Abbott also cited the shooter's criminal history.

"We must keep guns out of criminals' hands," he said.

The Austin American-Statesman reported that the gunman was arrested for evading arrest and criminal trespass in McLennan County in 2001, when he was 18, and received deferred adjudication — a form of probation — after pleading guilty to both misdemeanor charges. In Texas, only convictions for felonies or domestic violence misdemeanors block people from legally buying a gun.

Abbott could not be immediately reached for comment.

In Texas, licensed dealers must conduct background checks through the National Instant Criminal Background Check System, or NICS. However, there are exceptions to this rule, such as if the buyer already has a Texas license to carry a handgun. Private sales between individuals also do not require a criminal background check, which includes some gun sales at gun shows.

Also on Monday, Odessa Police Chief Michael Gerke said the gunman had been fired from his job just before the shooting. Gerke said the gunman and his boss at an oilfield services company got into a verbal altercation and both the gunman and the company called 911 to report the incident. The gunman also called the FBI's tip line, Gerke said.

FBI Special Agent Christopher Collins said the gunman was "rambling" but not threatening when he called the tip line.

The shooting spree began 15 minutes after that call when two Texas Department of Public Safety troopers pulled over the man for a traffic violation and he shot and wounded one of the troopers with a rifle. He then began driving around Midland and Odessa, randomly shooting at people. At some point he ditched his car, fatally shot a 29-year-old U.S. Postal Service letter carrier and continued shooting people from the postal van.

Correction: A previous version of this story incorrectly stated one of the exceptions to the NICS background check requirement. Holding a state license to carry a handgun is an exception to the requirement.