The theft occurred as the 2005 Porsche Carrera GT was being towed from the accident scene Saturday night, Los Angeles County sheriff's officials said.
The investigation led detectives to Jameson Witty, 18, who was arrested at his home in Los Angeles and was being held on $20,000 bail, the Sheriff's Department said in a statement. A second suspect, a 25-year-old man whose name has not been released, was outside California and arranging to surrender, the statement said.
Witnesses told investigators that they saw someone driving behind the tow truck that was hauling away wreckage hours after the fiery crash that killed Walker and friend Roger Rodas, who was driving the car and also died.
The witnesses said a man got out of the car when the truck was at a stoplight, grabbed the part, and drove away.
Detectives identified the two suspects, and while serving a search warrant at a home in Canyon Country, a community north of Los Angeles, they found a red T-top roof panel from the Porsche, sheriff's officials said. They would not say what led them to the two men or what evidence they had against them.
Sheriff's detectives planned to meet with prosecutors to discuss charges.
It wasn't clear if Witty has an attorney, and no phone listings for family or associates could be found.
Walker, who starred in all but one of the six "Fast & Furious" blockbuster films that glorified fast cars and dangerous driving, was killed when the Porsche smashed into a light pole and tree then caught fire on Saturday afternoon, authorities said. The seventh installment of the movie series was on a break from shooting for the Thanksgiving holiday.
Sheriff's investigators are still trying to determine what caused Rodas to careen out of control and crash.