Charges to Be Sought in Fatal Fire : Sylmar: Police are expected to seek a murder case against a woman who allegedly started a blaze that killed an infant.

Los Angeles police are expected to ask the district attorney to file murder charges today against a Sylmar woman who detectives said set a tenant’s house afire, killing a 6-month-old baby, in a minor neighborhood dispute.

Richard Robles was killed Wednesday morning when flames mysteriously erupted in a cottage behind a home at 13501 Borden Ave. in Sylmar, police said. The baby’s parents, Ricardo Robles and Virginia Portillo, rented the cottage from Raquel Lopez, 46, who was arrested on suspicion of murder.

Los Angeles Police Lt. Larry Hinrichs said the motive for the fatal fire was “a neighbor dispute of a minor nature.” He declined to elaborate.

Hinrichs said it was unclear whether Lopez knew the baby was in the dwelling when she allegedly used a flammable liquid to start the fire. Arson investigators on Thursday had not released the exact cause of the blaze.

Los Angeles County coroner’s spokesman Scott Carrier said that an autopsy would be conducted today to determine the cause of the baby’s death.

The baby’s parents were both at work when the blaze broke out. At the time, Portillo’s oldest daughter was watching her own two children and her stepbrother, Richard Robles, but she was not in the cottage when the fire began, fire officials said.

Rey Gonzalez, an off-duty Los Angeles city firefighter, was leaving a Sylmar grocery store when he spotted a cloud of smoke. Gonzalez said he hurried to the cottage and found a neighbor was using a garden hose to extinguish the blaze, which had engulfed the front half of the house.

Gonzalez rushed to the rear of the house, where he discovered barred windows. He used a gardening tool to pry the bars off. But by that time the fire and smoke had reached the rear of the cottage, and he could not get into the room where the infant was.

“All I could do was try and it didn’t work. . . . It was a sad feeling,” Gonzalez said. “But it makes it worse to find out that somebody set the fire. There’s a lot of unanswered questions.”

Lyn Mark, a next-door neighbor, said she heard popping and crackling noises, and when she looked over she saw smoke pouring from the cottage. “I turned my garden hose on to where the smoke was coming,” Mark said. “The flames surged out . . . my hose was like spitting on the fire.”

Firefighters arrived moments later. They extinguished the blaze in 10 minutes and discovered the baby’s body.

Mark said that on previous occasions she had heard fights between Lopez and the baby’s parents, including one night when she heard Lopez yelling at a crying Portillo.

But things were different on Wednesday night, she said.

“I didn’t sleep very well because it was so quiet over there,” Mark said. “I used to hear the baby crying at night when the mother put him to bed.”