Last week charred human remains were found at Campos' home in Hemet. Tests are being done to determine if the remains belong to the two teens.
Police also found a machete, butcher knives, a bullet casing, burnt clothing and an empty gas canister at the home. They recovered what was later identified as a charred right human foot in the back yard.
Campos, Rios and 17-year-old Felicia Sharp were first reported missing November 17. Sharp was brought to the police station by her parents on Wednesday. She has been interviewed by police, but details obtained in that interview haven't been released.
The name of the person of interest has not been released.
The Associated Press contributed to this story.