In order for an officer to stop your vehicle and initiate and investigation, they must first have probable cause to do so. An officer cannot make the initial traffic stop leading to the DUI without having a valid reason to do so. An officer cannot stop your vehicle just because he or she is having a bad day, doesn't like the color of your car, or is bored and wants something to do.
Probable cause is a flexible standard and its existence will be determined by a judicial officer. The officer will need to show the judge that he had a reasonable belief that a crime was taking place and that you were the person committing the crime. In practical terms, in order for an officer to stop you for DUI he or she must have observed you committing a traffic violation.
One common reason for which an officer may stop a vehicle that is not valid is profiling. Sometimes, an officer will run license plates to check whether or not the vehicle owner has a history of violations. While this may seem acceptable to the layperson, it does not rise to the level required to establish probable cause. A history of violations in and of itself is not enough for the officer to stop you without anything further.
Also, it is possible for officers to make a mistake about which vehicle committed the violation which was the basis for initiating the stop. For example, if there are similar looking vehicles and the road is busy, an officer may become confused about which vehicle was actually speeding. If there was no offense underlying the stop, then the resulting DUI charges may be set aside.
Proving that the arresting officer made an illegal stop leading to your charges can be very difficult. Judges generally rely on the officer's discretion. This is why it is important to hire an attorney to help you fight to protect your rights. An attorney can help you present a successful argument that the stop was illegal if that is the case. If you have been charged with a DUI in Arizona, where the laws are especially tough, its important to hire a seasoned professional who can protect your rights. DUI attorneys in Phoenix will know what you are facing. DUI attorneys in Arizona are able to navigate the laws and represent you during this difficult process.