A jury this summer found Castrillo guilty of first-degree murder for killing Merced taxi driver Dean Barker in 2015. He was charged with the crime shortly after he and another man, Dante Woods, called barker's cab company for a ride.
Attorneys said Castrillo shot Barker in the head three times.
Woods testified he saw Castrillo pull out the gun and shoot Barker.
The defense has said it plans to file an appeal.