OK, below is one of the criminal code sections that would presumably be charged in Montana. Note that the amount of the damage inflicted makes a very signficant impact on the penalty. If the damage is greater than $1500 (which is not hard to do on a car), one could be looking at 10 years and $50k in fines, plus the amount of the damages.
45-6-101. Criminal mischief. (1) A person commits the offense of criminal mischief if the person knowingly or purposely:
(a) injures, damages, or destroys any property of another or public property without consent;
(b) without consent tampers with property of another or public property so as to endanger or interfere with persons or property or its use;
(c) damages or destroys property with the purpose to defraud an insurer; or
(d) fails to close a gate previously unopened that the person has opened, leading in or out of any enclosed premises. This does not apply to gates located in cities or towns.
(2) A person convicted of criminal mischief must be ordered to make restitution in an amount and manner to be set by the court. The court shall determine the manner and amount of restitution after full consideration of the convicted person's ability to pay the restitution. Upon good cause shown by the convicted person, the court may modify any previous order specifying the amount and manner of restitution. Full payment of the amount of restitution ordered must be made prior to the release of state jurisdiction over the person convicted.
(3) A person convicted of the offense of criminal mischief shall be fined not to exceed $1,500 or be imprisoned in the county jail for any term not to exceed 6 months, or both. If the offender commits the offense of criminal mischief and causes pecuniary loss in excess of $1,500, injures or kills a commonly domesticated hoofed animal, or causes a substantial interruption or impairment of public communication, transportation, supply of water, gas, or power, or other public services, the offender shall be fined an amount not to exceed $50,000 or be imprisoned in the state prison for a term not to exceed 10 years, or both.
(4) Amounts involved in criminal mischiefs committed pursuant to a common scheme or the same transaction, whether against the public or the same person or several persons, may be aggregated in determining pecuniary loss.
(5) A person convicted of or who forfeits bond or bail for committing an act of criminal mischief involving property owned or administered by the department of fish, wildlife, and parks is subject to an additional penalty as provided in 87-1-102(2)(e).
Now, if the person went INSIDE the vehicle, there is an additional charge that can be added:
45-6-202. Criminal trespass to vehicles. (1) A person commits the offense of criminal trespass to vehicles when the person purposely or knowingly and without authority enters any vehicle or any part of a vehicle.
(2) A person convicted of the offense of criminal trespass to vehicles shall be fined not to exceed $500 or be imprisoned in the county jail for any term not to exceed 6 months, or both.
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