ODESSA, Texas (AP) — A Texas state trooper was the first to be shot. He pulled over Seth Aaron Ator for failing to signal a left turn, not knowing that Ator had just lost his job or that he was carrying an AR-style rifle.

From there, Ator sped more than 10 miles through the West Texas oil patch, shooting randomly from his sedan. His bullets struck a teenager at an auto dealership and a man outside a house on a quiet street. He also killed a mail carrier, then stole her Postal Service truck.

The unusual mass shooting — from behind the wheel of a car — spread terror over more than 10 miles (16 kilometers) through Midland and Odessa, two closely intertwined cities now brought that much closer by tragedy. The zig-zagging attack began along the oilfields that are the economic lifeblood of the region and cut into the neighborhoods where the petroleum boom has made housing expensive and scarce. It also tested local authorities, who have struggled to keep pace with the Permian Basin’s surging growth and were short-staffed over the Labor Day weekend when the attack began.

Another vigil for the seven people killed was planned for Tuesday evening in Odessa, where the same fear familiar to other cities struck by mass shootings has settled in.

“We had an active, rolling shooting, which kind of frightens me,” said Vicki Taylor, 67, a nurse who rushed out of her clinic Saturday to care for a woman bleeding from a bullet wound in her arm. “So now are we going to be scared every time we stop at a stoplight? Every time we walk into 7-Eleven? Every time we walk outside on a sidewalk? Are we going to look at people differently? Because he probably looked like anybody else driving in a car, but he had an assault rifle.”

Police ended the Labor Day weekend rampage when they finally cornered and killed Ator outside a crowded Odessa movie theater. Authorities said Ator was first pulled over at 3:13 p.m. on Interstate 20 and was killed about an hour later, at 4:17 p.m.

Seventeen minutes after the traffic stop began, Midland Police Sgt. Michael Wilson sent an email with the subject line “ALL HANDS NOW.” He said Tuesday that the department had been short-handed, and trying to find Ator was made more difficult by the fact that not all law enforcement agencies were communicating on the same radio channel.

Roaring down the interstate toward Odessa, Wilson saw what looked like an accident up ahead. Instead, it was another shooting victim.

“The reality of it is we’re following a trail,” Wilson said. “This is not a simple ‘I shot a cop and I’m on the run.’ This is way worse.”

The assailant’s route seemed as random as the people he targeted: a trucker driving home to his family and a father sitting at a traffic light with his two kids.

Authorities have described the chase down the highway and into the heart of Odessa as a different kind of mass shooting to contain. Ector County Sheriff Mike Griffis said Odessa, population 120,000, has struggled to keep up with the influx of new residents and acknowledged it “would have been nice to have some more personnel on the street” to stop the gunman sooner.

“We generally are short staffed, and in fact, when I heard all this going down, I got a hold of my captain, and I told him to get everybody on the street that had a vehicle available and let’s find this guy,” Griffis said.

FBI agent Christopher Combs said Ator had been on a long downward spiral, even before getting fired from his oil-services job Saturday morning. Ator called 911 both before and after the shooting began, and Combs said Ator also phoned the FBI tip line, making “rambling statements about some of the atrocities that he felt that he had gone through.”

But authorities said Ator did not make any threats in those phone calls.

He obtained his rifle through a private sale, allowing him to evade a federal background check that previously blocked him from getting a gun in 2014 due to a “mental health issue,” a law enforcement official told The Associated Press.

The official spoke to the AP on Tuesday on condition of anonymity because the person was not authorized to discuss an ongoing investigation. The person did not say when and where the private sale took place.

At some point, Ator failed a background check for a gun, federal officials said, but they have not revealed when or why. Online court records show Ator was arrested in 2001 for a misdemeanor offense that would not have prevented him from legally purchasing firearms in Texas.

Longtime residents of the region say the arrival of so many outsiders and so much oil wealth has caused communities that once felt like small towns to take on the challenges of bigger cities. Prices have risen and so has crime.

“I remember when this was bare land,” Amber Machuca, 31, said of the hotel where she works. “With the oil fields, it’s like a roller coaster and for us that live here. It’s just something we have to deal with.”

Ator lived on the outskirts of Odessa, in a ramshackle shed with corrugated metal walls. Combs described it as a “strange residence” that reflected “what his mental state was going into this.”

Plywood was apparently used to make additions to the shack, creating a small upstairs room perched on one corner of the structure like a turret.

A neighbor, Rocio Gutierrez, said Ator would shoot from the elevated space at night and was sometimes seen carrying bloody rabbits. Gutierrez said her family moved into a trailer in the area five months ago and lived in fear of their neighbor.

“He was a violent, aggressive person. He never said hello,” Gutierrez told The Associated Press. “We saw him every day. In the morning, we would say hello to him, because he was our neighbor, but he didn’t even turn around.”