Authorities are trying to figure out why a man stopped for a traffic violation in northwest Texas went on a shooting spree as he sped down highways Saturday. The latest U.S. mass shooting left seven people dead.

Twenty-two more were wounded in the rampage outside Odessa, including three officers. The alleged gunman was killed by police, bringing the total death toll from the incident to eight. The deceased ranged in age from 15 to 57.

It was the second mass shooting in Texas in a month.

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The terrifying chain of events began with a traffic stop Saturday on an interstate in the heart of Texas' oil country. State troopers say the man, a white male, pulled over for the traffic stop but then opened fire and took off.

Gunshots hit a trooper in the car that stopped him. The gunman then ditched his car and hijacked a postal service truck, unleashing more rounds as he drove away. Authorities later said the postal worker, 29-year-old Mary Granados, was killed.

Her teary-eyed identical twin sister, Rosie, told CBS News correspondent David Begnaud, "He could have taken the car without having to kill her. ... He didn't have to take my sister."

The gunman was eventually killed in a shootout with police outside a crowded movie theater, but two more officers were among those left wounded. All three officers shot were said to be in stable condition. At least 10 victims remained in critical condition at two local hospitals.

Odessa police said in a statement that the suspect fired "at innocent civilians all over" the city. The youngest victim confirmed as of Sunday was a 17-month-old girl who was struck by shrapnel.

Authorities said the death toll might have been even higher if the shooter hadn't been stopped when he was. At a news conference Sunday, "Law enforcement officials speculated the suspect may have planned to continue shooting inside the Cinergy Movie Theater in Odessa before the hijacked U.S. Postal Service vehicle he was driving was disabled by law enforcement officers," The Associated Press said.

The suspect died in a hospital in Midland and has been identified as Seth Ator, 36, according to his criminal record obtained by CBS News.

CBS Dallas reports that Ator was fired from his job with an Odessa trucking company Saturday morning just hours before the shooting. But sources close to the investigation told the station they don't believe his firing was what set him off, and that nothing worth noting was found when a metal shack connected to Ator was searched.

Seth Ator, 36-year-old suspected gunman in August 31, 2019 mass shooting in Odessa and Midland, Texas CBS News

Officials said during a news conference Sunday afternoon that they didn't believe there was any connection to foreign or domestic terrorism in the shooting. They said it appeared the gunman acted alone.

Police confirmed Sunday that the Texas shooter used an AR-15 "type weapon," but they didn't disclose any information on how it was obtained.

A law enforcement source told CBS News the suspect was pulled over by police because he apparently had been driving erratically. A number of calls came in to the Texas Department of public safety from people reporting his erratic driving, leading to the dispatch of officers.

"This was a joint effort by a multitude of departments to find this animal and to bring him to justice," Odessa Police Chief Michael Gerke said. He refused to utter the gunman's name.

Begnaud noted that the shooting came just a month after a gunman in El Paso killed 22 people when he opened fire in a Walmart store. Saturday's attack was the 38th mass shooting in the U.S. this year.

On Sunday, 10 new laws easing restrictions on guns took effect in Texas.

Speaking to reporters on the White House lawn Sunday, President Trump praised the first responders who intervened to stop the gunman Saturday, saying it "could have been worse."

He referred to the shooter as "another very sick person" and called the mass shooting a "mental problem."

Mr. Trump said the White House was continuing to work with lawmakers at new legislation on guns — work he said was going on irrespective of the latest atrocity. He repeated that mental health was in his view a "big problem" driving the country's spate of mass shootings.

Texas Governor Greg Abbott told reporters Sunday that "I have been to too many of these events" and added "Too many Texans are in mourning. Too many Texans have lost their lives. The status quo in Texas is unacceptable, and action is needed."