The only way deadly force would have been justified in the situation by the OP would have been if the trailer thief was driving at you with both vehicles while attempting to flee. (And how else would you be able to hit the radiator?)

After that, law or no, there would be extensive subjectivity involved - the local political and legal climate, how the local media report the incident, etc. And probably if you hit and stopped the vehicle with a single round vs. filling the local airspace with 18 projectiles...

__________________
Alan
SWCA LM 2023, SWHF 220