DAYTON, Ohio — Police worked Monday to pin down why a 24-year-old gunman killed nine people, including his sister, in a weekend shooting rampage in a popular nightlife area in Dayton, Ohio.

Connor Betts was wearing a mask and body armor when he opened fire with an AR-15-style rifle in the bustling Oregon District early Sunday before he was gunned down by police. If all of the magazines he had with him were full, which hasn’t been confirmed, he would have had a maximum of 250 rounds, said Police Chief Richard Biehl.

“It is fundamentally problematic. To have that level of weaponry in a civilian environment is problematic,” Biehl added.

Betts’ rampage was the second mass shooting in the U.S. over the weekend, both leaving a total of 31 people dead and more than 50 injured.

Of the more than 30 people injured in Ohio, at least 14 had gunshot wounds; others were hurt as people fled, city officials said. Eleven remained hospitalized Monday, Fire Chief Jeffrey Payne said.

Still unknown is whether Betts targeted any of the victims, including his 22-year-old sister, Megan, the youngest of the dead.

“It seems to just defy believability he would shoot his own sister, but it’s also hard to believe that he didn’t recognize it was his sister, so we just don’t know,” Biehl said.

While the gunman was white and six of the nine killed were black, police said the speed of the rampage made any discrimination in the shooting seem unlikely. It all happened within 30 seconds, before police officers stationed nearby fatally shot Betts.

Police have said there was nothing in Betts’ background that would have prevented him from buying the rifle he modified and used in the shooting. They said they also found a shotgun in his car.

Authorities identified the other dead as Monica Brickhouse, 39; Nicholas Cumer, 25; Derrick Fudge, 57; Thomas McNichols, 25; Lois Oglesby, 27; Saeed Saleh, 38; Logan Turner, 30; and Beatrice N. Warren-Curtis, 36.

Conflicting accounts of Betts have emerged, especially from his time at Bellbrook High School, southeast of Dayton.

High school classmates said he was suspended for compiling a “hit list” of those he wanted to kill and a “rape list” of girls he wanted to sexually assault.

Both former classmates told The Associated Press that Betts was suspended during their junior year at Bellbrook High School after a hit list was found scrawled in a school bathroom. That followed an earlier suspension after Betts came to school with a list of female students he wanted to sexually assault, according to the two classmates, a man and a woman who are both now 24 and spoke on condition of anonymity out of concern they might face harassment.

A former cheerleader, the woman said she didn’t really know Betts and was surprised when a police officer told her during her freshman year that her name was included on a list of potential targets.

“The officer said he wouldn’t be at school for a while,” she said. “But after some time passed, he was back, walking the halls. They didn’t give us any warning that he was returning to school.”

The male classmate, who was on the track team with Betts, said Betts routinely threatened violence toward other students.

“Most people avoided him,” the man said. “He would say shocking things just to get a reaction. He enjoyed making people feel scared.”

The discovery of the hit list early in 2012 sparked a police investigation and, according to a Dayton Daily News story at the time, roughly a third of 900 Bellbrook students skipped school one day out of fear of a planned attack.

Another former Bellbrook student, who also spoke on condition of anonymity due to concerns of harassment, recounted to AP that he was on a school bus when a uniformed police officer came on board, asked for Betts by name and then escorted him off.

It’s not clear what became of that investigation. Police Chief Michael Brown in Sugarcreek Township, which has jurisdiction over the Bellbrook school, wouldn’t answer any questions about Betts from an AP reporter Monday. Asked about a hit list in high school, the chief said “I don’t know anything about that.”

Later, Brown’s department emailed media outlets “everything we have on Connor Betts.”

The file included a 2015 crash report from when Betts ran his car into a ditch and a copy of a 2012 Ohio state law that requires all sealed records of juvenile crimes to be expunged either after five years or on the offender’s 23rd birthday. Department officials did not respond to questions about whether those records still exist.

Ohio law also bars anyone convicted of a felony as an adult, or convicted of a juvenile charge that would have been a felony if they were 18 or older, from buying firearms.

Though Betts, who was 17 in 2012, was not named publicly by authorities as the author of the hit list, the former classmates said it was common knowledge within the school he was the one suspended over the incident.

Drew Gainey was among those who went on social media Sunday to say red flags were raised about Betts’ behavior years ago.

“There was an incident in high school with this shooter that should have prevented him from ever getting his hands on a weapon. This was a tragedy that was 100% avoidable,” he tweeted.