Common law

This is the original and historical source of criminal law in the United States. It remains the primary source overall.

Statutes

All 50 states have their own penal codes. Therefore, for any particular crime somewhere, it would be necessary to look it up in that jurisdiction. However, statutes derive from the common law. For example, if a state's murder statute does not define "human being," that state's courts will rely on the common-law definition.

Model Penal Code

The Model Penal Code

Model Penal Code

The Model Penal Code is a statutory text which was developed by the American Law Institute in 1962. The Chief Reporter on the project was Herbert Wechsler. The current form of the MPC was last updated in 1981. The purpose of the MPC was to stimulate and assist legislatures in making an effort to...

 ("MPC") was created by the American Law Institute

American Law Institute

The American Law Institute was established in 1923 to promote the clarification and simplification of American common law and its adaptation to changing social needs. The ALI drafts, approves, and publishes Restatements of the Law, Principles of the Law, model codes, and other proposals for law...

 ("ALI"). In other areas of law, the ALI created Restatements of Law, usually referred to just as Restatements. For example, there is a Restatement of Contracts and a Restatement of Torts

Restatement of Torts, Second

The American Restatement of Torts, Second is an influential treatise issued by the American Law Institute. It summarizes the general principles of common law United States tort law...

. The MPC is their equivalent for criminal law.

Many states have wholly or largely adopted the MPC. Others have implemented it in part, and still others simply reject it. However, even when it is not adopted, it is often cited as persuasive authority in the same way that Restatements are in other areas of law.

Theories of punishment

Principle of legality

This is an overarching concept in American criminal law. People may not be punished for committing immoral or unethical acts. They can only be punished if that act has been announced beforehand as a crime.

Burden of proof

In the United States, the adversarial system

Adversarial system

The adversarial system is a legal system where two advocates represent their parties' positions before an impartial person or group of people, usually a jury or judge, who attempt to determine the truth of the case...

 is used. The prosecution must prove each element of the alleged crime beyond a reasonable doubt for conviction.

Voluntary act

Ordinarily, a voluntary act refers to commission. However, as discussed below, some crimes do punish failure to act.

Status

A status is not a voluntary act. For example, no law will be constitutional that makes it a crime to be addicted to illegal drugs, as opposed to using them, as happened in Robinson v. California

Robinson v. California

Robinson v. California, 370 U.S. 660 , was a case in which the Supreme Court of the United States held that the use of civil imprisonment as punishment solely for the misdemeanor crime of addiction to a controlled substance was a violation of the Eighth Amendment's protection against cruel and...

.

Omission

Failure to do something can occasionally be criminal. For example, not paying one's taxes is criminal. Typically, the criminality of failing to act will be codified.

Status relationships

Certain relationships create a duty to act at common law, such as spouse to spouse, parent to child, or employer to employee, for example.

Contractual duty

A person may contract to act, such a a babysitter to render aid in the event of the child in her care hurting himself.

Creation of risk

A person typically has a duty to act when he is responsible for putting the other in peril in the first place, such as through accidental injury.

Creation of reliance

A personal may have a duty to act when he begins to act but then stops. This situation typically arises in the hypothetical where a person is drowning. One bystander among many starts swimming out to rescue him but simply changes his mind halfway and decides to turn around and go back to shore alone. The rationale for making the bystander culpable is that the other bystanders did nothing because of his act. If the bystander had been the only person around, he would not be causing others not to assist, so he would not be culpable.

Social harm

Criminal law is distinguishable from tort law or contract law, for example, in that society as a whole is theoretically damaged. Obviously, there are particular victims, but society as a whole is the party responsible for the case against and, in the event of a conviction, punishment of the criminal. Social harm is that part of the crime that is sought to be avoided.

General intent

General intent is an awareness of all factors constituting the crime; including attendant circumstances. The person must be aware that he is acting in a proscibed way and be aware of a high likelihood that attendant circumstances will occur.

The requisite intent may be inferred from the doing of the act.

Specific intent

A specific intent crime requires the doing of an act coupled with specific intent or objective. Specific intent cannot be inferred from the doing of the act.

The major specific intent crimes are:
Conspiracy (intent to have crime completed), Attempt (intent to complete crime - SI or not), Solicitation (intent to have person commit crime), Embezzlement (intent to defraud), First Degree Premeditated Murder (premeditation), False Pretenses (intent to defraud), Forgery (intent to defraud), Larceny & Robbery (intent to permanently deprive other of interest in property taken), Assault (intent to commit battery) and Burglary (intent to commit felony in dwelling).

Justification

Justification defenses are full defenses. Society essentially tells the actor that he did nothing wrong under the circumstances.

Self-Defense

An accused will typically raise this defense when he is defending a crime of battery or homicide.

Non-Deadly Force

Under common law, a person may use non-deadly force to defend himself from a non-deadly attack under certain circumstances. For one, he may not be the aggressor. Moreover, he must believe his force is necessary. Furthermore, that belief must be reasonable. In addition, the person must be facing imminent and unlawful force.
Notably, the force the person uses need not be actually necessary. It need only appear so to a reasonable person.

Deadly Force

Under common law, a person may use deadly force to defend himself from a deadly attack under the same circumstances as for a non-deadly attack plus one additional one. The additional requirement is that a person may not use deadly force if non-deadly force would suffice.

Excuse

Excuse defenses are also full defenses. However, society is not saying the actor did nothing wrong, only that it will not punish him under the circumstances.

Homicide

Only a human being can commit a homicide (as opposed to other legal persons, such as corporations). He does so when unlawfully he kills another human being. There are two categories of homicide, murder and manslaughter.

Malice aforethought

There are four ways to satisfy the element of malice. One is an intent to kill and is the only form of express malice. Another is an intent to inflict great bodily harm. A third is a reckless disregard for the value of human life, sometimes called depraved heart. The last only applies when someone dies during the commission or attempted commission of a felony. It is often called the felony-murder rule and only requires the person to intend to commit the underlying felony. These last three types of malice are implied.

Degrees

Degrees of murder did not exist under common law. Most states have statutorily created at least two degrees of murder. Usually, a person only commits first-degree murder when he has express malice. If he has any other type of malice, he usually commits second-degree murder.