Early Thursday morning, the memorial to Andy Lopez was partially burned. The Central Fire Authority in Sonoma County says a burning candle likely ignited the 10-foot-long wooden altar.
Fire Chief Doug Williams said there had been speculation someone had purposely started the fire early Thursday.
The teen was killed last October while holding an air-soft rifle that police say Sonoma County sheriff's deputy Erick Gelhaus mistook for an AK-47 assault rifle.
Community activists believe rebuilding the shrine helps make sense of the teen's death.
"Before the memorial was burned down two nights ago there were rosaries, there were toys that Andy had played with, his favorite soda, his favorite potato chips, and things like that," said Jonathan Melrod with the Justice Coalition for Andy Lopez. "And to the community, this is a way of showing that Andy's life was not in vain, that it goes on and will continue."
The shooting prompted community outrage and several demonstrations.
The teen's family has since filed a federal lawsuit alleging civil rights violations.
(The Associated Press contributed to this report)