COVINA, Calif.  A man in a Santa Claus outfit opened fire on a Christmas Eve gathering of his in-laws in this Los Angeles suburb and then methodically set their house ablaze, killing at least eight people and injuring several others, the authorities said Thursday.

Shortly after the attack, the gunman, identified as Bruce Jeffrey Pardo, 45, killed himself with a single shot to the head at the home of his brother in the Sylmar section of Los Angeles, the police said.

In addition to the eight people whose bodies were found in the ashes of the house here, none of whom were identified, at least one other person was thought to be missing, and perhaps as many as three. Among the total of dead or missing were the couple who owned the home and their daughter, the estranged wife of the gunman, the police said.

Investigators continued to search the charred structure Thursday, and coroners said dental records would be needed to identify some of the remains.

The frenzied shooting occurred just before midnight Wednesday at the two-story house, set on a cul-de-sac in this middle-class town about 22 miles east of Los Angeles. Lt. Pat Buchanan of the Covina Police Department said Mr. Pardo, armed with one or two handguns and fire accelerant, had gone to the house looking for his former wife, Sylvia, with whom he was finalizing a contentious divorce after only a year of marriage.

People who escaped the house got out by smashing through glass and jumping. One woman broke an ankle when she leapt from a second-floor window.

Image Bruce Pardo, identified as the gunman.

The house was owned by James and Alicia Ortega, an elderly couple who were retired from their spray-painting business and who often invited their large extended family over for parties, particularly around Christmas.

Relatives said about 25 people, among them many children, were inside the home celebrating when Mr. Pardo knocked on the door around 11:30 p.m. He had apparently disguised himself as a hired entertainer for the children in order to gain access.

When a guest opened the door, Lieutenant Buchanan said, Mr. Pardo stepped inside the house, drew a semiautomatic handgun and immediately started shooting, beginning with an 8-year-old girl who was hit in the face but who survived, as did an older girl who was shot in the back.

As Mr. Pardo unleashed a barrage of gunfire in the living room, relatives smashed through windows, hid behind furniture or bounded upstairs. Then he sprayed the room with accelerant, using a device made of two pressurized tanks, one of which held pressurized gas. Within seconds, the house was ablaze.

Joshua Chavez of Seattle was visiting his mother’s house, which sits behind the Ortegas’, when he heard a loud explosion. “Then I saw black smoke and this large flame,” he said.

Mr. Chavez ran out to the backyard and heard three girls, including the one who had been shot in the back, trying to climb over his mother’s wall. “There’s some guy shooting in there,” he said one of the girls told him.

“About 20 seconds after that,” he continued, “the house was totally on fire. One girl said that a guy dressed as Santa started shooting.”

Image The attack occurred during a Christmas Eve gathering. Credit... The New York Times

Another neighbor, Jeannie Goltz, 51, saw three more partygoers fleeing the burning home. One of them, a young woman, had escaped upstairs from the living room but broke her ankle when she jumped out a second-story window.

SWAT teams arrived shortly after Ms. Goltz had shepherded these three survivors into another neighbor’s house, but by that time Mr. Pardo was on his way back to Los Angeles.

Police officers said they could not recall so horrific a crime in Covina, and neighbors said they would never have imagined anything so grisly on their quiet block.

The Ortegas had lived in the house for more than two decades and were known for their family spirit, their generosity and their dog, which frequently escaped their yard.

“I would generally play Santa for the family every year,” said Pat Bower, a neighbor of the Ortegas for 25 years. “The family was always together. Brothers and sisters, aunts and uncles were always in the house. They were a gigantic family. We all envied them, actually.”

Robert and Gloria Magcalas lived next door to the Ortegas for 11 years but were celebrating Christmas Eve with relatives in Los Angeles. Their own home was barely spared the flames.

“They were a big, loving family,” Mrs. Magcalas said. “We usually exchanged gifts with them today. They gave us tamales and cookies every Christmas.”

The police said they had found two handguns in the ruins, and an additional two pistols at the scene of Mr. Pardo’s apparent suicide. Officials said they would continue to search the crime scene Friday, seeking information about the identities of the dead.