ALLEN, Texas — It took four minutes for a neo-Nazi with an arsenal of firearms to kill eight people and wound seven others at a Dallas-area shopping center before a police officer ended the rampage, likely saving untold lives.

The massacre Saturday sent hundreds of shoppers at the Allen Premium Outlets scrambling for cover in shops, storerooms and closed hallways. Those killed included two elementary school-age sisters, a couple and their 3-year-old son, and a security guard who had helped others escape.

Allen, a multicultural suburb of 105,000, is left as the latest U.S. community rent by an eruption of violence in a year that has seen an unprecedented pace of mass killings.

Investigators say they have yet to establish a motive and that the gunman had no criminal record. But they've acknowledged the authenticity of a social media account on which he displayed a fascination with white supremacy while offering what are, in retrospect, chilling hints of his research and planning.

Here's what to know about the shooting at the Allen Premium Outlets.

How did the shooting unfold?

The gunman stepped out of a silver sedan on Saturday afternoon and started shooting people, cars and glass storefronts in a rain of bullets from an AR-15 style rifle — one of eight legally purchased firearms authorities said he brought to the mall.

Witnesses recalled hearing dozens of shots as shoppers stampeded for shelter and store workers pulled people into backrooms and rolled down metal gates for protection.

“We started running. Kids were getting trampled,” said Maxwell Gum, a 16-year-old pretzel stand employee. “My co-worker picked up a 4-year-old girl and gave her to her parents.”

Outside the locked rooms, security guard Christian LaCour had just helped someone get to safety and was trying to evacuate others when he was fatally shot, Allen Police Chief Brian Harvey said at a news conference Tuesday.

An Allen police officer who happened to be nearby saved “countless lives” by killing the gunman within four minutes of the attack's start, authorities said.

Shoppers sheltered inside storerooms for an hour or more as police cleared the sprawling mall shop by shop. As they were allowed to leave, some walked past bloodied bodies on the ground.

Fontayne Payton, 35, who was at H&M when he heard gunshots, recalled seeing small corpses covered in white towels and praying that they weren't children. “It broke me when I walked out to see that,” he said.

Who were the victims?

The neo-Nazi’s victims represented a cross-section of the increasingly diverse Dallas suburbs.

Sofia Mendoza, a second-grader at Cox Elementary School, and her big sister, fourth-grader Daniela Mendoza, were among them. Principal Krista Wilson called them “the kindest, most thoughtful students” in a letter to parents. Their aunt, Anabel Del Angel, said their mother was wounded.

“The girls have left a void that nothing in the world could ever fill. Please pray for their mom, my sister, and her broken heart,” Del Angel wrote in a fundraising post verified by GoFundMe.

Three members of a Korean American family were killed: Kyu Song Cho, 37, and Cindy Cho, 35, and their 3-year-old son. Another son was wounded. Kyu Cho was a managing partner at the law firm Porter Legal Group. “He was loved and respected,” the firm said.

LaCour, the 20-year-old security guard, was known to stop by the mall's Tommy Hilfiger clothing store.

“He was very young, very sweet, came in all the time to visit with us,” said the store’s assistant manager, Andria Gaither, who fled the gunshots Saturday.

Aishwarya Thatikonda, 26, was from India, the daughter of a judge in Hyderabad. She held a graduate degree in construction management and worked as a civil engineer at the Dallas-area firm Perfect General Contractors.

“She came to the United States with a dream to make a career, build a family, own a home and live forever in Dallas,” company founder Srinivas Chaluvadi said in an email.

Authorities identified the eighth victim as 32-year-old Elio Cumana-Rivas.

Who was the shooter?

Police said the gunman was Mauricio Garcia, who had lived in Dallas.

Garcia, 33, left a long trail of online posts describing his white supremacist and misogynistic views. He described mass shootings as sport, and posted photos showing his large Nazi tattoos and a favorite passage in the Hunger Games books marked with a swastika drawn in green highlighter.

He was Latino, and posted one cartoon image showing a Latino child at a fork in a road, with one direction labeled “act black” and the other, “become a white supremacist.”

“I think I’ll take my chances with the white supremacist,” he wrote.

Other posts show Garcia had visited the mall weeks before he began shooting and researched when it was busiest — the same time and day as his attack.

An Army official told The Associated Press that Garcia failed to complete basic training and was kicked out for mental health reasons. The official spoke on the condition of anonymity to discuss personnel matters.

Neighbors of the family home where he lived until recently said they thought he worked as a security guard. Authorities confirmed Tuesday that Garcia had an expired license as a security guard but said it was unclear where he'd worked.

Garcia lived in a motel in the months before the shooting. He posted videos online where he described, in mind-numbing detail, the contents of his living quarters, from the posters on the wall to his shower curtain.

In one video, a rat scurries across the cluttered room.