SAN DIEGO -- Investigators believe the Paradise Fire and at least 15 other blazes set in the same part of Valley Center over the last seven years were probably started by one or more serial arsonists, 10News reported.

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The Paradise Fire burned more than 56,000 acres, destroyed 220 homes and killed two people. The worst of the earlier fires occurred in 1996, blackening 400 acres around what is today Harrah's Casino.

All the fires were traced to a 5-acre area where the Paradise Fire began, Capt. Gary Eidsmore of the California Department of Forestry told the Los Angeles Times.

Eidsmore said the investigation is far from complete and that officials are still gathering evidence.

He said the case being developed is based largely on interviews with more than 50 people, some of whom were in the area on Oct. 26, when the Paradise Fire started.

These witnesses have led investigators to the belief that two or three people might have set the Paradise Fire together, Eidsmore told the newspaper. Officials are not sure of a motive or whether those who set it knew the fire would get out of control, the newspaper reported.

Investigators have officially classified the Paradise Fire as arson and are expected to issue a reward up to $10,000 for information leading to the conviction of whoever set the blaze.