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Under MO Implied consent laws, in pertinent part:
577.020. 1. Any person who operates a motor vehicle upon the public highways of this state shall be deemed to have given consent to, subject to the provisions of sections 577.019 to 577.041, a chemical test or tests of the person's breath, blood, saliva or urine for the purpose of determining the alcohol or drug content of the person's blood pursuant to the following circumstances:
(5) If the person, while operating a motor vehicle, has been involved in a motor vehicle collision which resulted in a fatality or a readily apparent serious physical injury as defined in section 565.002, or has been arrested as evidenced by the issuance of a uniform traffic ticket for the violation of any state law or county or municipal ordinance with the exception of equipment violations contained in chapter 306, or similar provisions contained in county or municipal ordinances; or
(6) If the person, while operating a motor vehicle, has been involved in a motor vehicle collision which resulted in a fatality or serious physical injury as defined in section 565.002.
So what the law says is that you cannot refuse and have deemed to have given consent to a test if there was a fatality under the implied consent law, but there is no mandatory testing required in all fatalities in Missouri, even though MADD is pushing for such laws.