Corpus deliciti (whether the government can prove you were the driver - I recently had a DUI dismissed for this very reason and my client was alleged to have blown a .219 on the BAC Datamaster)
Many DUI cases involve the accountability by the government of establishing Corpus Delicti "the body of the crime" meaning the driving element in DUI arrests. Many times multiple persons are located at the scene of a DUI investigation and the officer must determine who was driving. It is not unheard of for individuals to "take the hit" or "blame" for someone else, this is especially true with persons in relationships. The officer must then, but for any alleged admission to driving, establish by a scintilla of evidence who was driving. In many cases the officer will allege the individual had a seatbelt mark consistent with being involved in an accident, etc. Most corpus delicti cases involve accidents, but in those DUI cases which don't, it can be difficult for the officer to establish who was driving. My suggestion is to never speak with cops, your words will always get twisted.