There are two basic requirements to defining activity as a crime. 
1)  The activity must be forbidden by law (the law may also require something to be done).  2)  There must be some penalty attached to conducting the activity.

In every state, the legislatures have enacted criminal codes.  A state's criminal code is the primary place to determine what activities are crimes.  However, crimes may be defined in other places than the criminal code.  For example, in California, some crimes are contained in the Vehicle Code.

Federal crimes have been enacted and defined by Congress.  Again, however, some federal crimes are not contained in the United States Criminal Code.  Tax crimes, for example, are contained in the Internal Revenue Code.

There is therefore no one place to find all the crimes of a particular jurisdiction.  Also, many criminal laws have been interpreted by the courts.  Therefore, even a reading of a state's criminal codes will not give someone all the answers about how a crime is defined and what activity falls within that definition.

That is one of the many reasons a criminal defendant is entitled to a lawyer.  Someone who is uneducated in the law will have a very difficult time interpreting and understanding all the details that make up a law. 

Also, every crime that is defined in the law has two basic components: 
*an act, and
* a mental state 

In law, the Latin terms are used:  actus reas (act) and mens rea (mental state).  That concept, and specifically the contours of a criminal state of mind, is discussed further here.

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Generally, a defendant's or witness's out of court statements are not admissible to prove their truth in court.  This is the hearsay rule.  There are many exceptions to the hearsay rule, however, including an adoptive admission.

An adoptive admission is generally where the defendant, knowing the content of an accusation against him, adopts the truth of the accusation by his words or conduct.

This often comes up when the police plant someone in a jail cell with or next to the suspect.  The cellmate will ask the suspect questions about the crime.  The suspect may simply agree with the cellmate or may boast about his crimes. 

For example, let's say the defendant makes a statement, "Yeah, man, that guy didn't know who he was messing with."  That statement is admissible by itslef as an admission. But it becomes much more powerful as an adoptive admission when it is coupled with the cellmate's question, "You shot the guy because of the way he looked at you?"

Sometimes a defendant can adopt an accusation by his silence.  If someone is accused of a crime under circumstances where he could hear, understand, and reply to the accusation, and he does not respond, both the accusation and his response (or lack thereof) may be admitted in court.  The prosecutor can argue from this that the defendant admitted the crime.

Similarly, if the defendant responds to an accusation in a way that is evasive or equivocal, that can be admitted in court.

The factors to look for to determine if silence can be admitted as an adoptive admission include:
1.   whether the accusation was made in the defendant's presence;
2.  whether the defendant heard and understood the accusation;
3.  whether, in the circumstances, the defendant naturally would have denied the accusation; and
4.  whether the defendant could deny but didn't.

The idea behind an adoptive admission by silence is that most people, if falsely accused of a crime, would immediately deny it.  When someone does not deny it, that is an indication that the person has a guilty conscience.  A person's own words, or under these circumstances, their lack of words, can be powerful evidence against the defendant.

On an important note, if there is an indication that the defendant's silence was based on him invoking his right to remain silent under the Fifth Amendment, his silence cannot be used against him. 

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Corpus delicti is a latin phrase, which literally means, "body of crime."  In law, it is the principle that there must be evidence that a crime actually occurred before someone can be convicted of the crime.

The issue of a corpus delicti comes up when there is a confession to a crime.  If someone confesses to a crime, that person cannot simply be arrested and charged for that crime.  The police must first determine whether the crime actually occured.  (You might think this is a strange scenario, but people falsely confess all the time!)

Most states have a rule that a defendant's confession, standing alone, is not enough to prove him or her guilty beyond a reasonable doubt.  In fact, the defendant's statement may not even be admissible in court until the prosecution has first presented some other evidence that the crime occurred.  This is called corroborating evidence.

As an example, let's say someone walks in to the police station and confesses that he killed a prostitute ten years ago.  Based on the person's description of the crime (exactly when, where and how it occurred), the police would have to check old reports.  They would check if there were any prostitutes killed in the time, place and manner described. 

Or, if the body was never found, the police would have to look through missing person's reports from that time and place.  The confessing person may need to lead police to where the body was hidden or dumped or otherwise disposed of.  Although it is sometimes possible to convict someone of murder with no dead body, as discussed in a prior post, in a case like this, a body would almost certainly be needed.

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To aid and abet means to aid, help, facilitate, promote, instigate, or encourage another person to commit a crime.  The other person who commits the crime is called the direct perpetrator.

To be found guilty under a theory of aiding and abetting, the defendant generally must know of the direct perpetrator's criminal purpose, must intend to aid and abet the perpetrator, and must do or say something that in fact aids and abets the crime.

Someone who aids and abets a crime is generally just as guilty as the direct perpetrator.  This is true whether the aider and abettor had a minor role in the crime or was the most culpable person.

Examples of aiding and abetting include someone who is a lookout, who drives the getaway car, or who stays with the direct perpetrator during the crime as show of force or to help give the direct perpetrator courage to commit the crime. 

An aider and abettor can also be someone who orders the direct perpetrator to commit the crime (like a senior gang member directing a junior gang member to commit a crime).

The aider and abettor does not need to be present when the crime occurs.  On the flip side, mere presence at the scene of a crime, standing alone, is not enough to find someone guilty as an aider and abettor.

If someone only helps the direct perpetrator after the crime has been completed, such as by hiding the person, or destroying or disposing of evidence, that person is an accessory after the fact, not an aider and abettor.

If someone intends to aid and abet one crime, but a different crime occurs, the aider and abettor may still be guilty of that other crime, if the other crime was reasonably foreseeable under the circumstances.  This is called the natural and probable consequences doctrine.

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We hear about this all the time.  Someone is accused of a crime or suspected of a crime or charged with a crime.  They are brought into court or before Congress or into a grand jury.  They refuse to answer questions, invoking the Fifth Amendment. 

This can be called, pleading the Fifth, taking the Fifth, or invoking the Fifth.  It may also be called invoking you right to remain silent.  The witness can use any of these phrases, or they can say, "I refuse to answer on the grounds that it may incriminate me."  If the witness is worried about public perception, they may also insert the phrase, "On the advice of my lawyer..."

The Fifth Amendment of the U.S. Constitution states that no person "shall be compelled in any criminal case to be a witness against himself."

What this means is that the government has to build a case against you, using evidence that does not come from your mouth.  Of course, you can waive this right and talk to the police, and give them a bunch of evidence to use against you if you want.  And many, many people do exactly that.  But you have a constitutional right not to do so if you don't want to.

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I added an article about where to draw the line between simply thinking about or planning a crime, and doing enough to be convicted of an attempt.  What is an attempted crime?  Learn about what constitutes an attempt, as well as other criminal law concepts, in the Resources section.

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Most people are familiar with a trial jury.  A trial jury is usually made up of 12 people who listen to a trial and decide the defendant's guilt or innocence.  In law, a trial jury is called a "petit jury," to distinguish it from a grand jury. 

A grand jury has many differences and similarities with a trial jury.  The grand jury is generally much larger, often comprised of at least 23 people.  Like a petit jury, a grand jury is made up of regular citizens who respond to a jury summons. 

The  grand jury usually meets once a week for many months or even a year.  This schedule is different from a petit jury, which usually meets every court day until a trial is over.

The grand jury is an investigative body that can issue subpoenas for witnesses or documents.  The evidence is generally presented by prosecutors.  The grand jury reviews the evidence and determines whether a person should be charged with a crime, or indicted.  

A person being investigated, called "a target" of a grand jury, is not allowed to have an attorney present evidence to the grand jury.  Neither the target nor the target's attorney may be present in the grand jury proceedings unless subpoenaed (or ordered to testify).  

A target, if called to testify, or any other witness before the grand jury, may "plead the Fifth," or invoke their right to remain silent.  A person may not later be punished for remaining silent because it is a constitutional right.  Grand jury proceedings are kept secret until someone is charged.  It is therefore possible a target may not know he or she is being investigated.

Ostensibly, the grand jury's purpose is to prevent overzealous prosecutors from charging people with crimes without sufficient evidence.  However, in reality, grand juries usually follow the prosecutor's lead and do whatever the prosecutor suggests.

All federal criminal charges are made through a grand jury.  Many states use grand juries as well.  States are not required to use a grand jury.  States may use other means of "checking" the prosecutor's exercise of charging discretion.  For example, in California, prosecutors can use a grand jury, but they usually use a preliminary hearing instead. 

In a preliminary hearing, the prosecutor presents evidence before a judge, who must decide whether there is probable cause to believe the defendant committed the charged crimes.  A defendant may cross-examine witnesses and present evidence at a preliminary hearing, which is different than a grand jury.

The role of the grand jury is written into the U.S. Consitution.  The Fifth Amendment states in part, "No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a grand jury."

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