The suspect, Raymond Lee Oyler, 36, was already under arrest on suspicion of setting two other wildfires over the summer. Officials were investigating whether he was involved with more than three dozen fires since May.
Last week's blaze was the deadliest for firefighters since July 1994, when 14 were killed near Glenwood Springs, Colo., according to the National Interagency Fire Center statistics.
Before his arrest Tuesday, Oyler told his boss he was in trouble, reports CBS News correspondent Jerry Bowen.
"He pulled me to the side and said, 'Hey, I've got some problems,'" Jason Walden, of Highland Springs Automotive, said. "And he said, 'Well, they're actually investigating me for this fire over here.'"
District Attorney-elect Rod Pacheco said the evidence against Oyler was "overwhelming." Prosecutors charged him with five counts of murder, 11 counts of arson and 10 counts of use of an incendiary device. The charges include seven fires in June, one in July, one in September and two in October.
Oyler appeared in court in handcuffs and a jail jumpsuit as his attorney denied all charges. Oyler "adamantly denies involvement in this fire and in any of these fires," attorney Mark McDonald said outside court. "He's very distraught and scared ... The finger is pointing at him." Oyler, who said nothing during the brief hearing, was held without bail.
Authorities were checking whether Oyler was involved with a total of at least 40 fires in the area since May, according to an official involved in the investigation who spoke on condition of anonymity because the case is continuing.
Investigators were also looking at a 1998 fire in which the pilot of a firefighting aircraft died in a crash. That blaze burned more than 24,000 acres in the San Jacinto Mountains and had a burn pattern similar to last week's fire, the official said.
Authorities did not immediately disclose a motive and would not say what led them to Oyler.
Oyler will also face two so-called special circumstances, one alleging murders committed during arson and another alleging multiple murders.
The charges are punishable by life in prison without parole or the death penalty. Authorities will decide in the next 60 days which sentence to seek, Pacheco said.
"The feelings of the surviving family members of the victims will be consulted and be given great weight by our office in what is always a difficult decision," he said.
A woman who answered the phone at the home of Oyler's mother said she had no comment.
The fire was stoked by Santa Ana winds as it swept southwest through the San Jacinto Mountains about 90 miles east of Los Angeles. The flames overran the fire crew, destroyed 34 homes and charred more than 60 square miles before being contained Monday.
Three firefighters died at the scene, and a fourth died soon after at a hospital. A fifth was taken off life support and died this week.
Investigators interviewed Oyler on Oct. 27, served a search warrant on his residence Monday, then arrested him Tuesday.
"This arrest really does help with some of the closure, the healing that we in the Forest Service community, and in the families, need," said Jeanne Wade Evans, the San Bernardino National Forest supervisor.
Meanwhile, fire survivors met with officials last night to plan their recovery, reports Bowen. Since no tip led to Oyler's arrest, the victims may share the $500,000 reward fund to help rebuild their homes and lives.