MONTEREY PARK, California -- Detectives probing why an elderly Asian immigrant shot dead 11 people as they celebrated Lunar New Year at a dance hall in California are examining whether jealousy or a personal dispute was behind the tragedy, a report said Monday.

Huu Can Tran, 72, used a semiautomatic pistol in a rampage in the Los Angeles suburb of Monterey Park on Saturday night, killing men and women in their 50s, 60s and 70s. One person was shot in the parking lot.

He then drove to another dance studio where police say only the "heroic" actions of a young man who wrestled the weapon off him prevented another slaughter.

Hours later, Tran shot himself dead as police moved in on his white van.

Los Angeles County Sheriff Robert Luna said Monday that Tran, who had been arrested in 1994 for unlawful possession of a firearm, had fired 42 rounds in the attack.

But, he said, much was still unknown.

"We still don't have a motive, but we want to know the motive behind this tragic event," he told reporters.

"What drove a madman to do this? We don't know. But we intend to find out."

Detectives were looking Monday at Tran's previous connections to the two dance studios, with personal relationships a key area of interest, the Los Angeles Times reported.

Monterey Park resident Chester Hong told Agence France-Presse on Sunday he believed a domestic dispute over an invitation to a Lunar New Year eve party could be at the root of the attack.

"The wife (was) invited to join the party (but) the husband cannot be invited," he said. "And the husband may be upset and jealous."

Luna confirmed officers had been told Tran may have been known to some of his victims, but said there was currently no evidence he was related to any.

On Monday a picture began to emerge of a man who, according to his marriage license, had immigrated from China, and who had been a regular at the Star Ballroom Dance Studio in the past.

Tran's ex-wife told CNN the couple had met there two decades ago when he offered to give her informal lessons.

The woman, who did not want to be named, said they married a short time later, but the relationship did not last, with the divorce finalized in 2006.

She said Tran, who sometimes worked as a truck driver, was not violent, but could be impatient.

A man who said he had previously known Tran said he would complain about dance teachers, who, he claimed, would say "evil things about him," CNN reported.

He was "hostile to a lot of people there," the man told the broadcaster.

Detectives who searched a mobile home where Tran had been living in Hemet, 140 kilometers east of Los Angeles, recovered a rifle, electronics and ammunition, Luna said.

Police in the city said earlier this month Tran had made "fraud, theft, and poisoning allegations involving his family in the Los Angeles area 10 to 20 years ago."

Saturday night's mass shooting was the worst in the United States since a teenage gunman in Uvalde, Texas killed 21 people at an elementary school last May. All but two were children.

The toll from Monterey Park, one of California's largest Asian communities, rose to 11 on Monday when one of those injured in the attack died in the hospital.

The Los Angeles County and University of Southern California Medical Center said four victims had been treated at the hospital and one remained in a serious condition.

The coroner in Los Angeles said all of those who died were in their 50s, 60s or 70s, and named four of the dead as My Nhan, aged 65, Valentino Alvero, 68, Xiujuan Yu, 57, and 63-year-old Lilan Li.

Nhan's family said the tragedy was "still sinking in."

"She spent so many years going to the dance studio in Monterey Park on weekends," a statement said.

"It's what she loved to do. But unfairly, Saturday was her last dance.

"We are starting the Lunar New Year broken."

Amid so much heartbreak, stories of hope and heroism also emerged.

Security footage showed 26-year-old Brandon Tsay grappling with Tran in the lobby of the Lai Lai Ballroom & Studio in Alhambra as he tried to rip the MAC-10 9mm semiautomatic weapon from him.

"I lunged at him with both my hands, grabbed the weapon, and had a struggle," Tsay told ABC.

"He was hitting me across the face, bashing me in the back of my head, I was trying to use my elbows to get the gun away from him.

"Finally, at one point I was able to pull the gun away from him, shove him aside, create some distance, point the gun at him, intimidate him, shouting, 'Get the hell out here. I'll shoot. Get away. Go.'"

Luna praised Tsay, saying: "his heroic action ... saved countless lives."

"What a brave man he is." (AFP)