You don't need to prove he was over any limit to show intoxication. You would need to show he was "under the influence of an alcoholic beverage"
IC 321J.2
1. A person commits the offense of operating while intoxicated if
the person operates a motor vehicle in this state in any of the
following conditions:
a. While under the influence of an alcoholic beverage or
other drug or a combination of such substances.
b. While having an alcohol concentration of .08 or more.
c. While any amount of a controlled substance is present in
the person, as measured in the person's blood or urine.
True but that is going to be really difficult unless they have witnesses. They will need witnesses that could testify as to signs of him being under the influence of alcohol at the time of the accident.