Amy Smith suffers from insomnia and is being treated by a medical doctor specializing in sleep disorders. The doctor prescribes Smith sleeping pills to help her sleep. The instructions on the medication state that the dose should be taken with food and at least two hours prior to bedtime. Smith goes out to dinner with some friends at 8:00pm, after eating her meal she realizes that it is 8:30pm and she plans on going to bed around 10:00pm, so she takes her medication. Smith stays at the restaurant for another half hour before departing for home. On the way home, Smith stops at a grocery store to get some last-minute groceries and then heads home around 9:30pm. Before arriving at her residence, Smith falls asleep at the wheel and crashes her vehicle into a stop sign. The police arrive and begin their investigation, the officer observes Smith has slurred speech and slow drowsy movements, the officer believes Smith to be under the influence. Smith explains the sleeping pills and that is why she fell asleep. The officer arrests Smith for driving under the influence. How do you as the investigator prove voluntariness