The Marin County, Calif., teen, Max Wade, was separately accused of shooting at girl he was interested in and a romantic rival in 2012, and the subsequent investigation led to Fieri's stolen car.
The testimony Fieri gave only lasted a few minutes, in which he confirmed he does not know Wade and did not give him permission to drive the $200,000 car off the lot of a San Francisco dealership.
"It's been a really crazy story," Fieri said. "You never think a car like that is going to get taken from the dealership. I figured when we sent it down to them to get a warranty job that it would come back!"
Wade, 19, is charged with the theft of the car and attempted murder of a teenage girl.
Prosecutors say Wade drove the Lambo in a Mission Impossible-style heist to impress the girl, Eva Dedier.
Later, in April 2012, Wade allegedly drove a motorcycle alongside and opened fire on a truck carrying Dedier and her then-boyfriend, Landon Wahlstrom.
Deputy District Attorney Yvette Martinez told the jurors that Wade made a "cold, calculated decision to kill" when he fired five shots at Dedier and Wahlstrom as they sat in Wahlstrom's truck.
"If they hadn't ducked ... we would have had two dead teenagers," Martinez said.
Authorities tied a motorcycle helmet Wade purchased to the one seen on the shooter's head, and he became a suspect. Wade was then tracked to a Richmond storage facility in which they found the motorcycle and a revolver allegedly used in the shooting -- along with Fieri's yellow Lamborghini.
Fieri said that after the car went missing he received regular tips about the Lamborghini's whereabouts.
"We would get calls all the time, I mean all the time," Fieri said. "My friends would call me and say 'Listen, I just saw your car on the freeway.' And I'm like, ‘Believe it or not, there's more than one yellow Lamborghini probably in Northern California.' And people would call and we'd get reports, my attorney would hear about it. To come to find out that he was driving it, brave kid."
"There is no reasonable doubt," Martinez said. "He's guilty of all the crimes."