Hundreds of extra firefighters took to the streets of Los Angeles on New Year's Eve following a spate of arson attacks across the city.
Some 35 fires have been started since Thursday, mainly in vehicles parked outside homes.
The former Hollywood Hills home of the late The Doors singer Jim Morrison was among properties damaged as a result.
Police are puzzled by what the LA Times newspaper says is the worst wave of arson since the 1992 riots.
Two people were arrested on Friday, but were behind bars when new fires were started on Saturday.
Police are reportedly looking for a man who was driving a mid-1990s Lexus sedan.
But anonymous law-enforcement sources are quoted by the LA Times as saying the sheer numbers of fires over the last few days suggests some of the blazes could be the work of copycats.
The authorities say extra firefighters have been deployed to stations across Los Angeles.
Dozens of detectives have been assigned to the case, while a telephone hotline has been set up and more than $35,000 (£22,500) in rewards have been offered for information leading to a conviction.
"We're pulling out all the stops," LA Fire Department spokesman Brian Humphrey said. "We're hoping that the person or people responsible will be brought to swift and complete justice".
The spate of attacks began on Thursday night, with around 20 fires started in the Hollywood area of LA over the course of five hours.
In nearly every case, parked cars were the target, officials said.
Some of the fires spread to nearby buildings, including the home of the late Jim Morrison from where he wrote The Doors' song "Love Street".
A further 15 or so fires were reported overnight Friday into Saturday.
One couple in Sun Valley described to the LA Times how they woke at around 02:20 on Saturday morning after hearing windows shatter in their apartment block.
Steve Diaz, 26, and Michelle Villegas, 25, were helped to safety by firefighters but lost their car, which had been parked in the car port. Their flat, and several others, were badly damaged.
"As soon as we went out, the heat burned your face," Mr Diaz, a lab technician, said. "I don't know that it's even sunk in yet, what's happened."