Mo. Rev. Stat. § 563.070: Accidents an excuse for offense, when.

1. Conduct which would otherwise constitute an offense under chapter 565 is excusable and not criminal when it is the result of accident in any lawful act by lawful means without knowingly causing or attempting to cause physical injury and without acting with criminal negligence.

2. The defendant shall have the burden of injecting the issue of excuse authorized under this section.