He was ordered to pay £6,000 to his wife Sylvia, 43, who had moved out last spring.
Pardo was already behind with maintenance payments to his wife, who had three children from a previous relationship, after losing his job as an aerospace engineer in July.
When the door opened, Pardo fired the handgun at the eight-year-old daughter of Leticia Yuzefpolsky, a sister of Sylvia Pardo, as she ran to greet him, injuring her in the face.
He then fired indiscriminately at fleeing party-goers.
Pardo, 45, who killed himself after the massacre, had no criminal record or history of violence.
But police said he was angry at the terms of a divorce settlement last week which ended an acrimonious marriage that had lasted barely a year.
The perpetrator, 45-year-old Bruce Jeffrey Pardo, who entered the house wearing a Santa suit, committed suicide, dying from a gunshot wound to the head at his brother's residence in the early morning hours after the attack.
Authorities cited marital problems as a possible motive for the violence; reports indicated that Pardo's divorce had been finalized on December 18, one week before the massacre.
Witnesses saw Bruce Pardo use a metal device disguised with a Christmas bow to spray high-octane car-racing fuel around the home.Jan Gregory, a neighbour, said she saw a teenage boy running from the house and screaming: “They shot my family!” The house had been consumed by fire within seconds after Pardo doused the building with accelerant and torched it as he fled.Before he could flee, the vapour seems to have been accidentally ignited and exploded."Mr Pardo was severely injured during that explosion," said a police spokesman."He suffered third-degree burns on both arms, and it also appears that the Santa Claus suit he was wearing did melt on to his body."Bruce Pardo's ex-wife and her parents were among the victims as he stormed through their house firing two semi-automatic pistols.COVINA - It was a Christmas Eve massacre, a mass murder so chilling that it was unimaginable even to a 30-year veteran of the Covina Police Department.Investigators found nine bodies in the charred ruins of a home on a quiet suburban street Thursday and Friday. Wednesday, a gunman dressed as Santa Claus opened fire at a Christmas Eve party before burning down the house with a homemade flamethrower, officials said.He worked at the Jet Propulsion Laboratory in La Cañada Flintridge.He met Sylvia Pardo, previously Sylvia Orza, in 2004. PST, Bruce Jeffrey Pardo, dressed in a Santa Claus suit, knocked on the door of his former in-laws' house, occupied by about 25 people, with a gift-wrapped package containing a homemade flamethrower in one hand and a 9mm semi-automatic handgun in the other hand; he also had three additional 9mm semi-automatic handguns in his possession."I've been with the department for 30 years and I've never seen anything like this," Covina police Lt. Christmas for quiet Covina neighborhood will never be the same "They were met with a scene that was just indescribable," Covina police Chief Kim Raney said.The owners of the home at 1129 Knollcrest Drive, and their daughter, were believed to be among the victims, police said. Police discovered the body of the gunman, Bruce Jeffrey Pardo, 45, of Montrose, at his brother's home in the 15800 block of Joseph Court in Sylmar early Thursday.Police speculate that Pardo may have stood over and pointedly executed some of the victims, using the other handguns.Nine people died from either gunfire or flames, and three others were wounded: the eight-year-old girl who was shot in the face with severe but non-life-threatening injuries, a 16-year-old girl shot and wounded in the back, and a 20-year-old woman who suffered a broken ankle jumping out of the second-floor window.He had been due to act as an usher at the Christmas Eve midnight mass at his local church in Montrose, California.