The crime of driving under the influence (often called DUI, drunk driving, or DWI depending on the state), actually encompasses two different acts, both of which can result in severe and often unexpected consequences. The first act, as the name implies, is driving under the influence. In every state, it is illegal to operate a motor vehicle if your reflexes, coordination, or general mental functioning has been impaired by alcohol or some other type of drug (whether legal or illegal). This rule applies regardless of how much alcohol or other intoxicating substance you have consumed. The second act covered by drunk driving laws is the act of driving with a blood alcohol content (b.a.c.) greater than .08%, which, for the average person, is the equivalent of having roughly four drinks in your system. This rule applies regardless of whether your coordination, reflexes or mental functioning have actually been impaired.

It is important to understand that only one of these conditions is necessary to be arrested and convicted for a DUI, not both. In other words, a person who has a b.a.c. of .04% (half the legal limit), but whose coordination and reflexes are still impaired by that small amount, would be guilty of a DUI. Similarly, a person who has a b.a.c. of .10%, but who was not impaired at all by that amount, would also be guilty of drunk driving. In addition, all states currently have “zero tolerance” laws for drivers under the age of 21. This means that for these individuals, driving with any amount of alcohol in the blood, no matter how tiny, is illegal.

In addition to criminal penalties, drunk driving cases almost always carry with them administrative sanctions and other indirect consequences.Many states automatically suspend the drivers license of individuals arrested for DUI, and the suspension can remain in effect even if the person is later acquitted or the charges are dropped. Drunk driving arrests are also a common basis for denying insurance coverage, or for raising premiums to extremely expensive levels. Those convicted of drunk driving are usually ordered to attend "DUI schools", which are a combination of alcohol rehabilitation and victim impact classes, in which offenders are confronted with first hand accounts of the dangers of drunk driving.

Field sobriety testing

Because there are two distinct ways to violate DUI laws, police officers who suspect a person of drunk driving will test for both. These tests are commonly referred to as “field sobriety tests”, and they are technically a criminal investigation like any other. Field sobriety tests usually begin with the police officer asking the driver to perform a series of activities that are designed to reveal whether his or her cognitive ability has been impaired. Common examples are asking the driver to walk a straight line, stand on one leg, or recite a portion of the alphabet. The “horizontal gaze nystagmus” test is another procedure that is widely used by officers because it tests an involuntary reaction, meaning that its results cannot be faked. The test involves the officer holding a pen or other object up to the driver’s eye level, and directing the driver to focus on the pen as the officer moves it to the edge of their vision. If the driver has been drinking (or taken other intoxicating substances), their eyeball will bounce or jerk when trying to focus near the edges of vision, and the officer will be able to tell that the person is drunk.

Even if a driver “passes” the cognitive field sobriety tests, officers will often ask for consent to conduct a chemical test in order to investigate the second basis for DUI, unlawful blood alcohol content. The most common investigative technique for this purpose is the “breathalyzer”. The breathalyzer is a portable testing device that can detect a person’s blood alcohol content when they blow into it. Although the results are not considered reliable enough to be used as evidence in most courts, they can provide probable cause to take the driver to a hospital for a urine or blood test, which are highly accurate and usually admissible.

Although field sobriety tests are technically criminal investigations, drunk driving suspects do not have exactly the same procedural rights as other criminal suspects. Unlike most criminal suspects who are generally free to refuse a search of their body or property without a warrant, DUI suspects are subject to “implied consent” laws, which require them to consent to chemical testing or face an automatic license suspension. States are legally able to do this because driving is not technically considered a constitutional right, so the states are free to limit the practice as they see fit. In DUI cases, this means attaching the condition that if an individual wants to drive in that state, they have to agree to give a chemical test if asked.

In criminal trials, the burden of proof is always on the state. The state must prove that the defendant is guilty of all of the elements of the offense, beyond a reasonable doubt. Until this is done, the defendant is assumed to be innocent, and does not have to prove anything. In fact, it is not uncommon for a criminal defendant to simply remain silent, not present any witnesses or evidence, and argue that the prosecution did not meet its burden. However, these are instances where the defendant admits to committing the crime, but should not be punished because of some mitigating circumstance, such as self-defense or insanity. In these cases, the burden is said to “shift” to the defendant, and they are required to essentially prove the truth of the facts they claim.

Although each jurisdiction has its own nuances when it comes to criminal procedure and trials, most cases follow a typical process. The first step in this process is, of course, the commission of the crime and notification of the police. The police may investigate the crime and eventually make an arrest, once they believe they have probable cause to believe that the suspect committed the crime. Once taken into custody the suspect is “booked”, which means his name and indentifying information are recorded, his fingerprints are taken, he is photographed and searched, and placed in a holding cell.

The next step is the charging phase. During this phases, the prosecuting attorney will review the statements made by the arresting officer and any other witnesses, and determine whether the suspect should be formally charged with the crime. The prosecutor may charge the crime as described by the arresting officer, charge a completely different crime or no crime at all.

Once a charging decision has been made, the suspect, who is now officially a defendant, must be brought before a judge for an initial hearing, or “arraignment”. The purpose of this hearing is to ensure that the Defendant is aware of exactly what he is being accused of, and what his rights are as a criminal defendant. In most cases, the Defendant will be required to plead to the charges. It is also at this hearing that the judge assigns bail. The amount of bail required typically depends on the seriousness of the crime he is accused of, as well as how likely the judge believes he is to flee. If the Defendant cannot come up with enough money to make bail, he must wait in jail until his trial.

The next steps can vary greatly depending on the jurisdiction and the type of crime. In most misdemeanor cases, a judge reviews the allegations and available evidence, and determines whether the accused can be made to stand trial for the crime. In most felony cases however, the government must obtain an indictment by a grand jury before proceeding to trial. A grand jury is a body of people who evaluate (and in some states gather) evidence, in order to determine whether a person should stand trial. Grand juries meet in secret, and only the prosecutor is allowed to present evidence or argument. In general, a defendant has no procedural rights in a grand jury review. If the grand jury determines there is enough evidence to put the accused on trial, it will hand down an indictment.

Once an indictment or complaint has been filed, and arraignment has occurred, the prosecutor and defense attorney will conduct pre-trial proceedings. This typically means plea bargaining, by which the Defendant offers to plead guilty in exchange for reduced charges or a favorable sentence. This is also the step in the process that defense attorneys may attempt to bring pre-trial motions to try to get certain evidence suppressed, or the charges dismissed altogether.

After all pre-trial matters have been disposed of, the parties proceed to the focal point of the criminal process, which is of course the trial. Although the Constitution guarantees the right to trial by jury, some defendants choose to have their guilt or innocence decided by a judge, in what is referred to as a “bench trial”. After evidence is presented and the attorneys make their arguments, the jury meets in private to determine its verdict.

The U.S. Constitution provides for due process protections in all criminal investigations, beginning at the point a crime is discovered. The framers of the Constitution intentionally stacked the deck against the government in this process in order to make certain that innocent people are not wrongly convicted, as well as balance out the disparity in resources between the state and federal government, and the average accused person.

The foundation of these protections is the presumption of innocence, until guilt has been proven beyond a reasonable doubt. This burden of proof is often misunderstood, and can be difficult to quantify or explain. The reasonable doubt standard does not mean that a juror must be 100% certain of guilt, as this would mean that almost every criminal would go free at trial. However it also must mean something more than “more sure than not”. The Texas judiciary has defined reasonable doubt as "the kind of doubt that would make a reasonable person hesitate to act in the most important of his affairs.”

In addition to Due Process, the Constitution also provides that “The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.” In making these guarantees, the Fourth Amendment raises issues about what is unreasonable, what exactly constitutes a search or seizure, and the definition of probable cause.

Probable cause means that an investigating officer has enough evidence to make him or her reasonably suspicious of a particular person. If an officer has probable cause, she can testify before a judge and obtain a warrant to search the suspect’s home or other property for evidence. In cases where an officer witnesses a crime taking place, or sees a suspect fleeing the scene of a crime, a warrant is not necessary. In those instances, the police may search the suspect, their vehicle, and any surrounding areas in order to preserve evidence or ensure their own safety.

A particularly controversial subject is the definition of “search” itself. The Supreme Court has held that no search occurs if an officer views and seizes evidence from any place they are lawfully entitled to be. So, for instance, the police are permitted to stake out residences and businesses to watch for evidence of criminal activity, although the extent to which they can use technology to aid them is an ongoing question.

A due process right that is not explicitly guaranteed by the constitution, yet nonetheless has been granted by the courts, is the right to counsel when accused of a crime. It is not totally settled when exactly an accused individual has the right to an attorney, but it is clear that the right extends to well before the trial phase. The Supreme Court has ruled that at a minimum, when an investigation shifts from a general inquiry into an unsolved crime to a suspicion of a particular person, that person must be informed of their right to remain silent, and their right to an attorney.

If a court determines that one or more of a Defendant’s Constitutional Rights were violated during the investigation or arrest, the court will order any evidence collected as a result to be suppressed. This remedy exists to give legitimate meaning to the Constitution (it would be meaningless if there were no consequences for violating it), and to deter police misconduct. This is known as the “exclusionary rule”, and although extremely controversial, it is in effect in every jurisdiction. In addition, the exclusionary rule applies to any evidence that was gathered lawfully, but would not have been discovered but for the constitutional violation. This is referred to as the “fruit of the poisonous tree” doctrine.

If the investigation leads to an arrest and trial, the Constitution provides several more guarantees. The first of those is the right to a speedy trial, by an impartial jury. Many states have a statutory requirement that the prosecution bring a person to trial within a certain number of days, or the charges must be dismissed. A defendant may choose to waive this right in order to prepare his own defense, but the waiver must be knowing and intelligent, and the defendant must be aware of the consequences of doing so.

Other important rights involved in the criminal trial are the right to confront witnesses, to compel the testimony of favorable witnesses, and the right against self-incrimination. The Fifth Amendment right against self-incrimination actually applies to all phases of the criminal law process, though it is most commonly thought of in the context of a trial. This right also extends to statements made by the Defendant in confidence to certain trusted people, such as a spouse, priest, doctor, or lawyer.

The final consideration in every criminal case is whether any defenses exist for the conduct. In other words, the person intended to commit the act, and followed through, but cannot be held responsible due to a legally acceptable defense. Insanity is a well known example. Other examples are self-defense, and the lawful exercise of government authority. All of these situations are referred to as “affirmative defenses”, meaning that they must be proven by the defendant. A prosecutor does not have to prove that someone was sane at the time she committed a criminal act, or that she was not acting in self-defense.

In the context of a criminal trial, a person is insane if he either A) is unable to understand that his conduct was wrong, or B) understands that his conduct is wrong but is unable to control himself. It is important to note that the insanity defense is only one of several potential ways in which a defendant’s mental health can be relevant in the criminal process. A person who is found by a court to be mentally ill can be involuntarily committed to a mental health facility, and if the court finds they are insane at the time of the trial, they can be found incompetent to stand trial. Both circumstances are distinct from the insanity defense at trial.

In cases where an individual is found Not Guilty By Reason of Insanity, he will be institutionalized until a doctor certifies that he is no longer a danger to society. Many states also allow for the alternative conviction of Guilty But Mentally Ill, by which the defendant can be found guilty and sentenced for the crime, but will do the term in a mental health facility instead of a prison.

Self-defense, or the justifiable defense of another person or property is another example of a criminal affirmative defense. Under our system of law, it is permissible to use physical force to defend oneself against an imminent and unlawful attack by another. The same principle applies to certain lesser degrees when defending another person, or one’s property. Different states vary on the allowable use of force, and under what circumstances it can be used. For instance, in some states, a person has a duty to attempt to retreat from the situation before using deadly force. In other states, one has no duty to retreat when defending their home or business, but must try to retreat is the confrontation is in public. Another general rule is that self-defense cannot be used by the instigator of the situation. So for instance, if Tom breaks into John’s house late at night, and John points a gun at him and is about to shoot, Tom cannot shoot John first and claim self defense.