A Lancaster man will spend the rest of his life in a California prison after admitting that he gunned down four people inside their home, set the building on fire and left three dogs to burn to death in a killing rampage motivated by a breakup, prosecutors said.

Miguel Diego Sandoval, 21, pleaded guilty to multiple counts of murder, attempted murder, animal cruelty, arson and evidence destruction Thursday morning as dozens of his victims’ loved ones looked on tearfully from the gallery of a downtown Los Angeles courtroom.

Prosecutors and the victims’ relatives said Sandoval broke into the Lancaster home intending to target his former partner, who wasn’t home. Wearing a mask, Sandoval instead shot his ex’s brother and sister, 24-year-old Janvi Maquindang and 29-year-old Christine Aca-ac, while they were in their beds. He then killed their significant others — Edwin Garcia, 24, and Matthew Montebello, 23 — before setting fire to the home, leaving three of the family’s dogs to burn alive.

Maquindang managed to escape the fire but died of his injuries at an area hospital. Garcia and Aca-ac “pleaded for their lives and he shot them anyway,” according to Jennifer Calhoun, the mother of Montebello’s best friend.

Sandoval’s ex, Dillon Maquindang, stood at a podium Thursday morning and decried the defendant for cheating on them, manipulating them and taking out his failures on Maquindang’s family.

“You changed my life in ways I never asked for. But you did not take away my ability to live, to love and to find happiness again,” Dillon said. “I hate that I’m giving you this much of my energy today. ... My family deserves to be remembered for who they were, not how they died.”

Dillon’s younger sister, Tahnya, was hiding in the home behind a locked door as Sandoval went on his rampage, according to the lead prosecutor on the case, L.A. County Deputy Dist. Atty. Alexander Bott.

Sandoval admitted to the brutal killings in a recorded jailhouse conversation, Bott said.

Speaking in court Thursday, Tahnya dismissed Sandoval as a “coward.”

“You’re too pathetic to deal with your own emotions that you had to plan something as miserable as this,” she said.

Sandoval sat forward as his victims’ relatives spoke, looking toward L.A. County Superior Court Judge Charlaine Olmedo rather than the people he’d wronged. The gallery was filled with the victims’ relatives, many of them wearing white T-shirts emblazoned with a picture of the victims and the phrase “forever in our hearts.”

Although his sentencing was delayed to a later date, Sandoval can only receive life without the possibility of parole or the death penalty under California law. The district attorney’s office did not seek capital punishment in the case.

Staring at the back of Sandoval’s head, Calhoun said the devastation he wrought on the night of the murders has reverberated for years since.

“It continues through every nightmare, every memory, every smell of smoke,” she said. “Every birthday that will never be celebrated.”