There are two cases running at the same time when a person is charged with Driving While Intoxicated in Missouri. They are the criminal case charging you with the crime of DUI or DWI and an administrative case solely regarding suspension of your license. In the criminal case the US Constitution applies and in the administrative case not so much. Also, there are different elements that must be proven and different levels of proof in the two cases.
In the criminal case all the elements of DUI or DWI must be proven and the investigation and prosecution from start to finish must comply with the constitutional limits on criminal prosecutions. If you were to be pulled over in for a traffic stop and arrested for DUI or DWI in violation of your constitutional rights then the prosecutor may not be able to win the criminal case. A possible issue could be the reason for the officer to stop you prior to the investigation for a DUI-DWI arrest. If the officer makes an illegal traffic stop that leads to a DUI-DWI arrest then a DUI-DWI lawyer can contest the criminal charge based on this issue and may be able to get the case dismissed. This is due to an invalid seizure of your person leading to evidence that could be considered unconstitutionally obtained. Also, your guilt must be proven to a neutral judge or jury to the level of beyond a reasonable doubt.
The administrative license case is a civil matter rather than a criminal case and therefore there are not the same constitutional restrictions, fewer elements that must be proven and the case only has to be proven to the level of preponderance of the evidence. The only two elements in an administrative license suspension for DUI-DWI is 1) whether there was a reasonable basis (same as probable cause) for the DUI-DWI arrest and 2) whether the person tested over .08% BAC (unless you are under age or hold a CDL). The basis for the traffic stop is not an element necessary to be proven in the administrative case. And, the constitution will not prevent illegally obtained evidence to be used in the administrative case in the same way as the criminal case. Based on the example above, if an officer makes an illegal traffic stop leading to probable cause for a DUI-DWI arrest the criminal case could be thrown out based on the invalid traffic stop but the administrative suspension could go forward.
The level of proof necessary in the two cases can cause a difference in outcome as well. The preponderance level of proof used in the administrative case just requires that the evidence shows the person arrested was more likely to have been intoxicated as not. This means 51% more likely than not. However, in the criminal case the prosecutor has to prove beyond a reasonable doubt that the person was Driving While Intoxicated. Beyond a reasonable doubt is much more than just 51% as likely. Based on this you can probably see how a case could fit in between the two levels of proof such that it doesn’t quite make it to the level of beyond a reasonable doubt but still be more likely than not.
As you can see, it is possible to lose your license after a DUI-DWI arrest even if you are not found guilty of the criminal charge of DUI-DWI. This does not happen very often but it occurs often enough.