Section 3.1: Sources of Criminal Law

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The term criminal law can be confusing, but it is an essential concept in the criminal justice system. Criminal law can refer to all laws dealing with the criminal justice system or just the substantive criminal law, which describes what acts are prohibited and what punishments are associated with those acts. Legal defenses, like the insanity defense, are also included in criminal law.

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Criminal laws are usually divided into two categories: misdemeanors and felonies. Misdemeanors are less serious crimes like petty theft, simple assault, disorderly conduct, and public drunkenness. They are usually punishable by a fine and less than a year in a local jail. Felonies are serious crimes like rape, murder, burglary, and kidnapping. They can be punishable by death or a long period of incarceration in a state-run prison.

Another way of classifying criminal law is based on the inherent evil of the act. If an action is “wrong in itself,” it is considered a mala in se offense. If an action is not necessarily evil and is only regarded as criminal because the government prohibits it, it is considered a mala prohibita offense. Victimless crimes are usually considered mala prohibita offenses.

Some crimes are more visible to the public, such as murder, and are referred to as visible crimes, street crimes, or ordinary crimes. Occupational crimes are less noticeable and involve crimes provided by a particular job, such as embezzlement. Crimes committed by groups with a discernable organizational structure are classified as organized crime.

Cybercrime is a relatively new category of criminal activity that involves offenses related to computers and related technologies, such as distributing child pornography, phishing, spreading viruses, and hacking into business computers.

Hate crimes are motivated by bias toward a particular race, religion, ethnicity, or sexuality. Understanding these various types of criminal offenses is essential for understanding the criminal justice system and the types of illegal activity that exist in society.

Criminal versus Civil Law

The legal system has two types of wrongs: civil and criminal. A civil wrong, known as a tort, refers to the harm done to another person. When a person wins a tort case in civil court, they may receive a monetary award called damages. This is because torts are considered private wrongs, meaning they are usually between two individuals and do not necessarily harm society as a whole.

On the other hand, a crime is considered a public wrong. This is because it harms not only the individual but also society as a whole. For this reason, all criminal prosecutions are brought forward in the name of the state, representing the people. Depending on the state, this can be called the people, the commonwealth, or some other term. The prosecutor, who works for the government on behalf of society, brings the case forward in the criminal justice system.

Understanding that the criminal and civil justice systems can interact is essential. This means that a person can be found guilty of a crime in criminal court and found liable for a tort for the same behavior. For example, a person who steals from someone can be found guilty of theft in criminal court and must pay back the stolen property in a civil case.

Additionally, individuals who have suffered losses due to criminal actions can sometimes use the civil courts to recoup their losses. For example, a hit-and-run accident victim can sue the driver for damages in civil court in addition to the criminal charges the driver may face in criminal court.

State versus Federal Crimes

The United States operates under a legal system called the common law system, meaning based on previous court decisions rather than solely relying on statutes. However, criminal laws today are primarily created through statutes, which are laws passed by elected officials in state and federal legislatures. These laws describe what actions are prohibited and what punishments are associated with those actions.

A critical difference between state and federal criminal statutes is that federal laws often have a jurisdictional element. This means that the law applies only to certain areas or activities within the country, such as those that involve interstate commerce. This limitation is due to the Constitution, which grants specific powers to the federal government and reserves all other powers to the states.

As a result, most criminal laws exist on the state level because the Constitution limits Congress’s authority to create criminal laws. However, this does not mean the federal government has no role in criminal law enforcement. Federal law enforcement agencies, such as the Federal Bureau of Investigation (FBI) and the Drug Enforcement Administration (DEA), can investigate and prosecute crimes that involve federal jurisdiction.

There is overlapping jurisdiction when an act is considered a crime on both the state and federal levels. This means that the individual could potentially face prosecution on both levels. While this is allowed by constitutional law, it is not a common occurrence. In practice, it is left up to the discretion of prosecutors to decide which jurisdiction to pursue a case in. In some cases, federal prosecutors may take over a case when there is a belief that the state court system has failed to deliver justice.

The primary function of substantive criminal law is to define crimes, including the associated punishment. Procedural criminal law sets the procedures for arrests, searches and seizures, and interrogations. In addition, it establishes the rules for conducting trials. Where does criminal law come from?

The Common Law

Common Law may confuse students because it has different meanings depending on the source. However, to understand its meaning, we need to delve into the history of the American legal system. Common law, or “judge-made” law, originated from judges deciding cases based on legal customs during medieval England. Initially, the law was not documented in writing and was passed down orally. 

By the end of the medieval period, some cases were recorded in writing, and judicial decisions were collected into books called reporters. English legal scholar Sir William Blackstone is credited with organizing much of the common law tradition of England into his four-volume set, Commentaries on the Laws of England, which the founding fathers brought to the colonies and incorporated into the laws of the United States.

Today, most crimes are defined by statute, but the definitions and ideas used in these statutes come from the common law tradition. Judges who interpret a statute still use common law principles for guidance. The definitions of some crimes, such as murder and arson, have remained unchanged from their common law origins, while others, such as rape, have undergone significant changes.

Precedent is a crucial feature of the common law tradition. The doctrine of stare decisis, meaning “to stand by things decided,” states that once a court decides on a legal matter, it is bound to rule the same way in future cases with the same legal issue. This doctrine ensures consistent rulings and equal treatment under the law.


The United States Constitution is one of the most important legal documents in the country. When the founding fathers drafted the Constitution, they created a blueprint for the government that outlined the powers and limitations of each branch. It is considered the supreme law of the land because it is the country’s highest authority on legal matters. The framers of the Constitution emphasized the document’s importance by stating in Article VI that it would be the supreme law of the land.

The Supreme Court, the highest court in the United States, has the power to strike down any law or government action that violates the Constitution. This power was established in the landmark case of Marbury v. Madison in 1803. This precedent means that the Supreme Court can nullify any law made by Congress or a state legislative assembly that does not meet constitutional standards.

All of the states in the country have their own constitutions that mirror the principles of the federal Constitution. They all have a system of checks and balances, three branches of government, and a Bill of Rights that outlines the protections afforded to citizens. All state laws are subject to review by the high courts of those states, and if a state law or government practice (such as police, courts, or corrections) violates the constitutional law of that state, it will be struck down by that state’s high court.

In addition to state constitutions, local governments also have their own laws and regulations that must conform to the state and federal constitutions. These laws and regulations are subject to similar scrutiny by the courts. It is important to note that the Constitution is a living document, and as society evolves, interpretations of its principles may change over time. The Supreme Court’s role in interpreting the Constitution helps to ensure that the document remains relevant and effective in guiding the country’s legal system.

Statutory Law

Statutes refer to written laws that are passed by legislative assemblies. Unlike common law, modern criminal laws tend to be a matter of statutory law. This means that most states and the federal government have moved away from the common-law definition of crimes and established their own versions through the legislative process. As a result, most criminal law today is made by state legislatures, with federal criminal law being made by Congress.

When presented with legislation, legislative assemblies tend to consider it as presented rather than in a specific order. This can make finding the law concerning a particular matter quite challenging. Almost all statutes are organized by subject in a set of books called a code to simplify the process of finding the law. The body of statutes that make up criminal law is often referred to as the criminal code or, less commonly, as the penal code.

The criminal code is typically divided into different categories of crimes, with specific provisions for each crime listed under its respective category. This makes it easier for lawyers, judges, and other legal professionals to identify the specific laws that apply to a particular case. These categories often include crimes such as murder, assault, theft, and fraud, among others.

It is important to note that statutes are not set in stone and can be changed or amended through the legislative process. As societal values change and new issues arise, lawmakers may create new laws or modify existing ones to reflect these changes. This allows the criminal justice system to remain adaptable and responsive to the needs of society.

Administrative Law

The branches of the U.S. government – executive, legislative, and judicial – are well-defined, but the picture becomes muddled when looking at government agencies and commissions. These organizations, also known as bureaucracies, are a mix of legislative and judicial in character. They can make rules that carry the weight of law, investigate violations of those laws, and punish those who break them. The Federal Trade Commission (FTC), the Internal Revenue Service (IRS), and the Environmental Protection Agency (EPA) are examples of such agencies. The rules created by these agencies that have the force of law are known as administrative law.

Administrative law differs from other types of law because it is not created by a legislative body such as Congress but rather by administrative agencies. These agencies are given the power to create and enforce rules related to specific areas, such as the environment or taxation. Administrative law can have a significant impact on businesses, individuals, and even government agencies themselves. It is often subject to judicial review to ensure consistency with the Constitution and other laws.

Court Cases

In the legal system, when higher courts (the appellate courts) decide on a legal issue, that decision must be followed in future cases that involve the same legal issue. This principle is known as the doctrine of precedence or stare decisis. In other words, the legal decision made by an appellate court carries the same weight as a law passed by a legislature. Such legal decisions are referred to as case law or common law.

The criminal justice community relies heavily on the appellate courts, particularly the Supreme Court, to assess and explain how statutory laws and government practices align with the requirements of the Constitution. This is important because the Constitution serves as the fundamental law of the United States and governs all other laws in the country. The legal principles derived from court cases are crucial in understanding how the criminal justice system works and how laws are applied in specific situations. These principles are essential for lawyers, judges, and other legal professionals to understand when interpreting laws and applying them to different cases.


The term criminal law refers to laws related to the criminal justice system, including substantive criminal law and legal defenses. Criminal laws can be divided into misdemeanors and felonies based on the severity of the crime. They can be classified as mala in se or mala prohibita offenses based on the inherent evil of the act. The criminal justice system can interact with the civil justice system, and the United States operates under a common law system based on previous court decisions and statutes. 

The Constitution is considered the supreme law of the land, and the Supreme Court has the power to strike down laws that violate it. Statutory law refers to written laws passed by legislative assemblies and is organized by subject in a code. Administrative law is created by administrative agencies and has the force of law. Court cases establish legal principles crucial in understanding how laws are applied in the criminal justice system.


Blackstone, W. (1776/2016). Commentaries on the Laws of England. Oxford University Press.

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Last Updated:  06/06/2023

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