Every case is different, but here are a few of the most common defenses to a criminal charge
In order to convict you of a criminal charge, the prosecutor must prove your guilt beyond a reasonable doubt. This is a pretty lofty standard, and during any trial the defendant may present a defense in order to raise such a reasonable doubt. Most defenses break down into one of two categories: (1) I didn't do it or (2) I did it, but I shouldn't be held responsible.
1. I Didn't Do It
The most basic defense to any criminal charge is to simply prove that you didn't do it.
Innocent Until Proven Guilty
One of the hallmarks of the American legal system is the presumption that you are innocent until proven guilty. This isn't just an ideal, it's an actual legal presumption, which means the judge and jury must assume you're innocent until they are shown otherwise. This is why a defendant can "plead the fifth," remain silent, and not offer a shred of evidence to support his or her claim of innocence and still prevail. It is the prosecutor's job to prove a defendant is guilty, not a defendant's job to prove that he or she is innocent. So what does a prosecutor have to show?
Beyond a Reasonable Doubt
The prosecutor must demonstrate to the judge or jury that there is no reasonable doubt of your guilt. If any reasonable doubt can be shown, any at all, then the prosecutor has failed and you should be found innocent. Because this standard is so high, most defendants concentrate on raising some reasonable doubt to the prosecutor's allegations.
I Have an Alibi
One of the primary ways defendants prove that they didn't do it is to demonstrate that they couldn't have done it. An alibi defense is evidence that you were somewhere else, often with someone else, and thus couldn't have been the perpetrator. By demonstrating to a judge or jury that it is likely that you weren't present at the crime scene, you are creating a reasonable doubt of your guilt.
2. I Did It, but Shouldn't Be Held Responsible
Many defendants admit that they did the act, but claim for one reason or another, that they shouldn't be held responsible. Here are a few examples of this type of defense:
This is a common defense when someone is charged with causing some form of physical violence (assault, battery, etc). The defendant flips the story, and demonstrates that rather than being the aggressor, he or she was actually the victim and was acting to protect themselves from harm.
Self-defense is an ancient defense that exists in most legal systems, and is predicated on the belief that people have a right to defend themselves from physical injury. Proving such a defense can be tricky since a defendant will generally have to demonstrate that self-defense was necessary, the belief of physical harm was reasonable, and that the response was reasonable. For example, responding to an assailant's threat to punch you by shooting them is almost certainly an unreasonable response.
Although it makes for fascinating TV dramas, in real life defendants rarely plead insanity as a defense. Judges and jurors are very skeptical of these claims, and because of the abstract nature of this defense, it can be very difficult to actually prove.
The theory behind an insanity defense is the notion that in almost every criminal law, there is a "mental" or "intent" element. Often, the required mental state is that you must have intended to perform the criminal act. If a defendant is precluded from an understanding of what they're doing because of mental illness, then they can't possess the mental state that the criminal charge requires. From a policy standpoint, we also tend to think that it would be more appropriate to send someone who is truly insane to psychiatric care, not to prison. Thus, even if a defendant is successful in an insanity defense, they will be sent to a psychiatric institution, not set free.
So how do courts define "insane"? The most popular definition is the McNaughten test which defines insanity as "the inability to distinguish right from wrong". To successfully win an insanity defense, a defendant will rely on testimony from a psychiatrist, and will undergo extensive psychiatric testing which can be painful and humiliating.
Under the Influence Defense
Related to the insanity defense, some defendants defend themselves by claiming that they were under the influence of drugs, and could not have had the mental state necessary to commit the crime. In other words, they were too high to really know what they were doing. Only a few states allow this defense, and even then, it is only a partial defense. At best, it will lower the crime you are convicted of to a lesser crime.
An entrapment defense is appropriate when an official induces you to commit a crime. Common examples of this are prostitution stings or drug sales. The theory is that the government shouldn't be allowed to push you into committing a crime and then convicting you for it.
This defense won't be successful if the judge or jury believes you were predisposed to committing the crime, however. So even if an undercover officer offered to sell you illegal drugs, if you have a history of drug use, then an entrapment defense isn't likely to be successful.
Get Legal Help Defending Yourself Against a Criminal Charge
Defending yourself against a criminal charge has many facets. No one individual can understand the full ramifications of every charge and every defense to a criminal case without a good criminal defense attorney. So if you're being investigated or charged with a crime, you'd be wise to seek out a local criminal defense attorney as soon as possible.