New details about the deadly shooting at a mall in Greenwood, Indiana, over the weekend were released Monday, including the identities of the three victims and the bystander who ultimately killed the gunman.

The alleged gunman, 20, opened fire with an AR-15-style rifle around 6 p.m. Sunday at the Greenwood Park Mall, located just south of Indianapolis, firing 24 rounds within two minutes before a Good Samaritan stepped in and killed the shooter, the city’s police chief, James Ison, said at a news conference.

The Johnson County and Marion County coroners' offices identified the slain victims as a married Indianapolis couple — Pedro Pineda, 56, and Rosa Mirian Rivera de Pineda, 37 — and Victor Gomez, 30, also of Indianapolis. A woman and a 12-year-old girl who was hit by shrapnel were wounded in the attack, police said.

The bystander was identified as 22-year-old Elisjsha Dicken, of Seymour, who was shopping at the mall with his girlfriend, Ison said. The chief called Dicken's quick action "nothing short of heroic."

POLICE SAY ‘GOOD SAMARITAN’ PREVENTED FURTHER LOSS OF LIFE IN INDIANA MALL SHOOTING: ‘TACTICALLY SOUND’

"He engaged the gunman from quite a distance with a handgun and was very proficient in that, very tactically sound," Ison said of Dicken. "And as he moved to close in on the suspect, he was also motioning for people to exit behind him."

Eli Dicken, the bystander who stopped the Greenwood Park Mall gunman

Elisjsha Dicken, 22, of Seymour, was identified as the bystander who shot and killed a gunman who opened fire Sunday at the Greenwood Park Mall in Greenwood, Indiana. (The Dicken Family)

Dicken fired 10 rounds from his handgun, according to the chief, and that as he fired, the gunman "attempted to retreat back into the restroom and failed, and fell to the ground after being shot."

"He's my lil brother," Dicken's brother Cameron told Fox News Digital on Tuesday. "And he’s an amazing kid and I’ve never been more proud of anyone in my entire life. What he did was selfless and amazing."

He continued: "And he did what he did because it was the right thing to do not for fame or glory but because he knew that he couldn’t just stand by and let it continue to happen."

Dicken’s attorney, Guy A. Relford, said his client acted heroically in a statement to Fox News Digital.

"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.

Greenwood Police Chief James Ison speaking

Greenwood Police Chief James Ison speak during a press conference at the Greenwood City Center in Greenwood, Indiana, on Monday. (AP Photo/Michael Conroy)

The gunman entered the mall and walked into a bathroom, where he spent about an hour before he emerged and opened fire, police said. Investigators believe he spent that time preparing and possibly assembling a disassembled rifle that he had brought in his backpack.

Greenwood Park Mall in Greenwood, Indiana

A truck blocks the entrance to the closed Greenwood Park Mall in Greenwood, Indiana, on Monday. (AP Photo/Michael Conroy)

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Investigators found a second AR-15-style rifle in the bathroom. They also found on the deceased gunman a handgun, a waistband holster and several magazines that contained more than 100 rounds of ammunition.

Greenwood, Indiana mall exterior shot

Police gathered outside a Dick's Sporting Goods in Greenwood Park Mall in Greenwood, Indiana, following the shooting on Sunday. (Facebook/@Ty J S)

Ison said the gunman, of Greenwood, was apparently facing eviction before opening fire at the mall, and the suspect's family did not have any indication that anything was wrong or that he may turn violent. 

The chief said investigators are still trying to determine a motive. 

The Associated Press contributed to this report.