The shirt that Magnum wears when his is in jail is different than the shirt before and after. The pattern doesn't match up along the buttons as well.
Magnum is approached by a mysterious stranger driving a Mercedes SUV at a gas station as he is filling up his tank. Neither vehicle has front license plates. Also, the SUV doesn't have a rear license plate visible as it departs. Hawaii requires both front and rear license plates on registered vehicles. Given the circumstances, Magnum should have noted the mystery man's license plate number as he drove away.