Investigations | Section 1.1


Fundamentals of Criminal Investigations

Adam J. McKee, Ph.D.


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Section 1.1: Criminal Law & Investigations 

A crime is an act or omission that is contrary to law for which there is some sort of formal punishment.  From a practical standpoint, a crime is simply a violation of some criminal law. Criminal law is the branch of law that seeks to prevent harm to society by prohibiting certain acts and omissions and punishing those who commit those acts or omissions. Because criminal law seeks to protect society as a whole, criminal prosecutions are brought forward in the name of the state, not in the name of the victim, as it would be in a civil law case.  Usually, the state’s case is argued by an attorney called the prosecutor.  The person who is accused of the crime is known as the defendant.

Sources of Criminal Law

In the United States, there are three primary levels of government:  local, state, and federal. Most criminal cases originate in violations of state law and investigated by local law enforcement.  Federal prosecutions make up only a small fraction of criminal cases. Thus, most criminal investigators will need to be concerned with the criminal law on the state level.  Most of these laws can be grouped into four major categories:

  1. Common law
  2. Statutory law
  3. Case law
  4. Administrative law

Common Law

Originally, the common law was the ancient traditional legal system of England.  When America was founded, the American colonists brought the common law with them to America.  That legal tradition is the basis of criminal law in most states (Louisiana being a notable exception).  The law was considered common because, being based on precedent, all citizens could expect similar treatment by the criminal justice system under similar circumstances.  The common law was first put on paper in the written opinions of judges, so laws originating in court cases are sometimes referred to as common law. Many modern criminal laws have their origins in the common law, as well as many legal ideas that define our contemporary legal system.

Statutory Law

A statute is a law passed by some legislative body.  This means the U.S. Congress on the federal level and the legislatures of each state on the state level.  The ordinances passed by local governing bodies also fall into this category. Many states have moved entirely away from the common law and now make the criminal law a matter entirely of statute.  These statutes are referred to as statutory law.  Statutes are generally passed in no special order by lawmaking bodies.  Usually, however, the statutes are organized into a set of books and arranged by topic.  Such a topical organization of statutory law is known as a code.  The section of a state’s (or the federal government’s) code that contains criminal laws is often called the criminal code or penal code.

Case Law

When most Americans think of lawmaking, they think of legislatures debating the merits of a proposed law and then taking a vote.  Less understood is the fact that American courts are also in the business of making law, albeit indirectly. Appeals courts have the power to interpret previous court decisions, statutes, regulations, and constitutional issues.  These interpretations are delivered to us in the form of written decisions called opinions. These decisions taken together form the body of case law that is binding on law enforcement and the lower courts.

Administrative Law

While the power of making laws rests in the hands of legislatures, legislators have long recognized the fact that they cannot be experts in everything and cannot adequately regulate certain aspects of our complex society.  For this reason, legislatures often delegate their lawmaking authority to administrative agencies that in turn promulgate rules and regulations. Many of these regulations have the force of law and carry criminal penalties (such as fines and jail time) when violated.  These agency rules and regulation are collectively known as administrative law.  

Classification of Crime

Most jurisdictions recognize that all breaches of the law are not equal.  That is, some offenses are far more serious than others. The more serious a crime is, the more cost the government is willing to pay to bring the offender to justice and the more severe the punishment.  The most serious general classification of crimes is as a felony. A felony is a relatively serious crime that is punishable by more than a year in prison.  A misdemeanor, on the other hand, is a less serious crime that is punishable by less than a year of incarceration, usually in a local jail or regional detention facility.

Elements of Crimes

Criminal law is usually a matter of statute.  The statute will set out what act is prohibited and what punishment is warranted for those who commit that act.  While each specific crime will be superficially different from another, there are certain common elements that will be found in nearly every crime.  Knowledge of these elements of crimes is essential to the investigator.  Because the prosecution must prove each element of the crime beyond a reasonable doubt in court, investigators must provide sufficient lawfully obtained evidence for this purpose.  Without knowledge of the elements of a crime, the investigator has no idea what evidence is valuable and what is worthless. Most laws follow a general form and have the same general elements in common.  Obviously, there must be a criminal act or omission.

An omission is something that the law commands and that the defendant fails to do.  Common examples of omissions are the failure to pay taxes and the failure of certain professionals such as teachers and nurses to report child abuse.  The idea is that not doing something commanded by law is a crime.  By tradition, the criminal act or omission is known by the Latin legal phrase actus reus.  Do not be misled by the use of the verb act—it is not necessarily an action verb.  Some passive states such as the possession of certain contraband items (e.g., drugs, automatic weapons, explosives) satisfy the criminal act requirements.

In our legal tradition, we generally do not punish accidents as crimes.  That is, a person that does not intend the otherwise criminal result of his or her actions is not culpable, or worthy of blame.  For a person to be guilty of a crime, they must have done it on purposely, or at least knowingly.  The idea of purpose is also known as intent.  These words are used to describe the mental state of the perpetrator at the time the act was committed.  This mental element of crimes is known by the Latin legal phrase mens rea.    

Most jurisdictions today punish those who engage in behavior that is likely to result in a prohibited harm even if the person did not actually intend the harm.  If the person knew the behavior was very risky and did it anyway, the mental state is considered reckless by law.  If the behavior was risky but the actor did not perceive the risk, then the act is considered to be done negligently.

Some crimes, usually violations, will not have this mental element.  Obviously, it would be detrimental to the working of the criminal justice system if officers had to go to court and testify as to the mental state of a person cited for illegally parking a vehicle.  Crimes that do not involve a mental element are known as strict liability offenses.  Full-scale investigations, however, usually involve serious felony crimes.  These types of crimes will usually involve a mental element that must be proven.  The task of proving what was going on in someone’s head seems daunting, and it sometimes is.

However (luckily for the investigator) there is a presumption of law in most jurisdictions that a person’s intent is the likely outcome of his actions.  For example, of Joe Doe shoots someone in the head, the law will presume that the likely outcome of shooting someone in the head is to kill them, so it follows that Doe intended to kill his victim.  Obviously, the mens rea of homicide is much more complex, and we will delve more deeply into that in a later chapter.          

For some crimes, the mental element coupled with the criminal act is sufficient to define the crime.  If those elements can be proven beyond a reasonable doubt, then a conviction is likely. Some crimes are more complex in nature due to the addition of other elements.  Some crimes require that a resulting harm occur.  In addition to the prohibited harm, it must usually be shown that the perpetrator’s criminal act (actus reus) was the cause of the prohibited harm.  In murder, for example, the resulting harm is the death of a person.  If no one dies, then you cannot have a murder (although attempted murder is a possible charge).

Keep in mind that if the circumstances of a case are not such that elements of one crime can be proven, then there may well be a less serious offense that can be proven.  When the elements of a more serious crime contain all of the elements of a less serious crime, then the less serious crime is considered a lesser-included offense of the first crime.  In many jurisdictions, for example, breaking and entering is a lesser-included offense of burglary.

Sometimes, even when all of the elements of a crime can be proven beyond a reasonable doubt, the defendant can still be exonerated if he can mount a successful defense.  Defenses come in three major varieties.  Procedural defenses are where the defendant uses some misbehavior by the criminal justice system to nullify a prosecution, such as claiming a speedy trial violation because the prosecutor did not move forward with the case quickly enough.  

Sometimes the criminal code will establish certain exceptions to crimes where, when proven, make the act noncriminal.  For example, killing another person is usually a criminal homicide. If, however, the killing is done is self-defense, the law will not punish it.  Such defenses are known as justifications.  This is why undercover narcotics officers are not committing crimes when purchasing drugs—they are covered under an execution of public duty defense.  The third and final major category of defenses is excuses.  Excuses are when circumstances are such that we are willing to forgive the defendant for his or her criminal acts.  Insanity is the most well-known of these.  

From this simplified overview of criminal law, we can establish several key pieces of evidence that the investigator will be looking for.  It is critical to find evidence that establishes:

  • That the criminal act (according to some statute) was committed
  • That the defendant was the one who committed the criminal act
  • That the defendant had mental state required by the statute
  • That (if required) the prohibited harm actually occurred
  • That the criminal act was the legal cause of the prohibited harm
  • That the defendant has no criminal defense available at law
Modification History

File Created:  05/02/2019

Last Modified:  05/02/2019

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This work is licensed under an Open Educational Resource-Quality Master Source (OER-QMS) License.

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