At approximately 11:30 p.m. 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 on a trolley and two 9mm semi-automatic handguns; he also had two additional 9mm semi-automatic handguns in his possession. Moments after the door opened, Pardo pulled out the two handguns and immediately shot his 8-year-old niece Katrina Yuzefpolsky, the 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. Police speculate that Pardo may have stood over and pointedly executed some of the victims, using the other handguns.
After the shootings, Pardo unwrapped the package containing the homemade flamethrower, and used it to spray racing fuel gasoline to set the home ablaze. 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. There was one survivor who called the authorities during the attack, after escaping to a neighbor's house. The resulting fire soared approximately 40 to 50 feet and took 80 firefighters an hour-and-a-half to extinguish. Due to the intensity of the fire, identification of the victims was done with dental and medical records.
After the attack, Pardo put on his street clothes and drove his Dodge Caliber rental car to his brother's house in Sylmar about 30 miles away from the crime scene, where he was later found dead from a self-inflicted gunshot wound. His brother was not present in the home at the time of Pardo's death. It was initially believed that Pardo intended to flee to Canada by plane since he had bought an airline ticket to a flight on Air Canada. However, it was subsequently discovered that the flight itinerary, on Northwest Airlines, was from Los Angeles to Moline, Illinois (with a layover in Minnesota). Pardo had called days before to tell a high school friend that he was planning to visit but investigators were unsure if he actually intended to visit or if the flight was to fool investigators. He had visited the friend before in October 2008. Other reports stated that the Santa suit had melted during the flamethrower portion of the attack and had adhered to his skin so not all of it could be removed.
However, suffering from severe third-degree burns on his arms stemming from the blaze, Pardo decided to go against the initial plan. Police found $17,000 in cash cling-wrapped on his legs inside a girdle. His rental car, parked one block from his brother's house, had been rigged with remnants of his Santa suit that would detonate the car with black powder if removed. Also recovered from the scene were four 13-round capacity handguns that were empty, and at least 200 rounds of ammunition. Suggesting that what had been inside the car was being treated as a threat, a bomb squad fired an incendiary device into it, burning and destroying it. At Pardo's house in Montrose, police had recovered five empty boxes for semiautomatic handguns, a Benelli M2 Tactical shotgun and a container for high-octane fuel tank gasoline. They also found what was described as a "virtual bomb factory" in his home.