America's latest rampage unfolded like many before it: A gunman entered a bustling public space, armed with high-powered weapons and an abundance of ammunition, and he opened fire into a crowd, killing several people.

But this most recent episode - at a shopping mall in Greenwood, Ind., on Sunday - did not end like the majority of mass shootings in this country, with the assailant's arrest, suicide or death at the hands of police officers.

Instead, an armed bystander engaged the attacker and killed him in a shootout, firing 10 rounds as shoppers fled the scene, authorities said. Three other people were killed and two were injured, including a 12-year-old girl, during the latest spasm of violence in what has been an unrelenting string of high-profile public mass shootings in recent months.

The Greenwood incident is unique, however, because it became one of the rare instances of an armed civilian successfully intervening to end a mass shooting, adding more fuel to a national debate about the role of bystanders during an active shooter attack.

"Many more people would've died last night if not for a responsible armed citizen that took action very quickly, within the first two minutes of this shooting," Greenwood Police Chief Jim Ison said at a news conference Monday afternoon.

Investigators identified the gunman as Jonathan Douglas Sapirman, 20, and they said his motive remains unclear but that he planned the attack. Sapirman arrived at Greenwood Park Mall with two rifles, a handgun and more than 100 rounds of ammo, police said, firing two dozen shots before 22-year-old Elisjsha Dicken killed him with a 9mm pistol. Dicken, who was shopping with his girlfriend, was "lawfully carrying" his weapon and is cooperating with the investigation, Ison said.

Advocates for expanding gun access frequently justify their positions by citing a scenario in which an armed civilian stops a shooter: "The only way to stop a bad guy with a gun is a good guy with a gun," the National Rifle Association tweeted on Monday. But in practice, this is an uncommon occurrence during mass shootings. In recent studies of more than 430 "active shooter incidents" dating back to 2000, the FBI found that civilians killed gunmen in just 10 cases.

Despite the data, Indiana this month lifted its permit requirement to carry a handgun in public over the objections of police officials, with the bill's author arguing that the move allowed "Mr. and Mrs. Lawful Hoosier" to "defend themselves in public."

"I think you might get more individuals carrying, sort of primed for something to happen, which is particularly dangerous," said Jody Madeira, a law professor at Indiana University Bloomington who researches the Second Amendment. "And I think also you'll get this idea that these people are needed out there to help protect citizens, when in reality that's the job of the police."

Because Indiana law does not require training to carry a firearm, it's more likely that bystanders will be underprepared to take on a shooter, Madeira said.

"I think there's a lot of alternative scenarios which do not end as well, which are very, very likely to come about rather than that one individual becoming a hero," she said.

Dicken does not have a police or military background, authorities said, but Ison called his movements "very tactically sound," pointing to the way he engaged the gunman from a distance then closed in while motioning for people to exit behind him.

After Dicken shot at him, Sapirman tried to retreat into a restroom but failed, Ison said. Dicken then approached mall security to identify himself.

Dicken's attorney, Guy Relford, said his client wouldn't comment extensively until the investigation is complete

"He is a true American hero who saved countless lives during a horrific event that could have been so much worse if not for Eli's courage, preparedness and willingness to protect others," Relford said in a statement.

Officials in Greenwood, a city of 60,000 just south of Indianapolis, were still struggling to process its new place on the terrible list of cities and towns rocked by mass shootings. The Sunday incident follows those at a July Fourth parade in Highland Park, Ill., a doctor's office in Tulsa, an elementary school in Uvalde, Texas, and a grocery store in Buffalo.

"This has shaken us to our core," Ison said.

Authorities identified the victims as Victor Gomez, 30, and the husband and wife pair Pedro Pineda, 56, and Rosa Mirian Rivera de Pineda, 37.

In an interview, Isabel Pineda described coming home from work Sunday evening to find her home surrounded by police cars and the agony that followed when officers told her that her father and stepmother died in the shooting.

Isabel and her three children live in the same house as the couple, who had gone to the shopping mall that day to have dinner together alone.

"He was the best dad and the best grandfather in the world," Isabel said through tears. "He didn't deserve this!"

Her father arrived in the United States in 2007, she said, fleeing poverty in El Salvador to try to offer his six children a better life. After years of hard work, he was able to bring them all to the United States, Isabel said. He loved fishing and playing with his grandkids. Isabel said her stepmother was a "great, kind woman" who treated Isabel's children "as if they were her own."

An investigation into the incident is still ongoing, but authorities on Monday released more information about Sapirman, who lived alone at an apartment less than a mile from the mall. He had a juvenile record with minor offenses, such as fighting at school, Ison said, but he had no criminal history as an adult.

Sapirman purchased both rifles from gun stores in Greenwood over the last two years, Ison said, and he frequented a nearby shooting range. The police chief added that Sapirman had recently resigned from a warehouse job and may have received an eviction notice.

When SWAT officers raided his apartment, they found a laptop alongside a can of butane gas in the oven, which was on a high temperature, Ison said. Bomb technicians retrieved the device, which the FBI will analyze, along with Sapirman's cellphone, which was dropped in a toilet at the mall, Ison said.

The shooting took place weeks after the state dropped its requirement for a permit to purchase and carry a handgun in public, joining 24 other states that allow permitless carry, according to an analysis by PolitiFact.

However, private businesses can still impose their own firearm restrictions. Simon Property Group, which owns Greenwood Park and other malls around the world, stipulates in its code of conduct that "no weapons" are allowed at its properties, though it notes that "exceptions to this code of conduct will be determined by local center management." When asked whether Greenwood Park Mall allows guns, the mall directed The Washington Post to its code of conduct.

Greenwood Park Mall said in an email Monday that it was "grateful for the strong response" from authorities, and it praised the bystander who stopped the gunman.

The permitless-carry bill sparked divisions even among Republicans in the GOP-held statehouse before Gov. Eric Holcomb, R, signed it into law in March. Police officials, including the state police chief and the Fraternal Order of Police, spoke out against the measure, saying the lack of a permit requirement would put officers at risk and undermine their ability to quickly determine whether someone was legally allowed to possess a gun.

Indiana is also one of 19 states with a red-flag law in place, which allows a judge to take away a person's gun if they are determined to be a threat to themselves or others.

Local leaders on Monday stressed the importance of unity in responding to their community's pain. Pastor Ryan Bailey, of Resurrection Lutheran Church in Greenwood, said his congregation is hosting a vigil for the victims so loved ones and residents can grieve together.

"A main challenge we face when trying to resolve or respond to this problem of gun violence is that we spend so much time apart from one another and we speak about it through social media and screen," Bailey said. "We are not coming together tonight to debate policies."

- - -

The Washington Post's Bryan Pietsch contributed to this report.