Standard of Proof in Law: Definition & Cases

Instructor: Brittany McKenna

Brittany is a licensed attorney who specializes in criminal law, legal writing, and appellate practice and procedure.

Standard of proof refers to the amount of evidence required to prove a legal claim or assertion. This lesson will introduce you to the different standards of proof and some of the cases associated with those standards.

Definition & Cases

Imagine that you are a newly licensed attorney. Your suits are pressed, your shoes are polished and you're ready for your first day on the job as a state prosecutor. After three years in law school, you know the ins and outs of making an argument in front of a jury. But there's the tricky issue of evidence. How much is enough? And how can you be sure that you're proving your case, while still respecting the constitutional rights of the accused?

Standard of proof describes the amount of evidence necessary to prove an assertion or claim in a trial. In the criminal justice system, the burden of proof lies with the government. This means that it is the obligation of the prosecutor, not the defendant, to prove its case and the elements of the crime charged. In civil cases, it is the plaintiff that has the burden of proof (although the burden may shift based on which party is making a claim).

Standards of proof define what the burden of proof is based on the claim asserted. Some standards of proof relate to events that take place before a suspect is even charged with a crime. These pretrial standards are very important because evidence obtained in violation of a suspect's constitutional rights will be thrown out, or suppressed.

Depending on the evidence at hand, it may be tough for you, the rookie prosecutor, to meet the proscribed burden of proof. Let's discuss the different standards and the circumstances under which each standard is applied.

Reasonable suspicion

Reasonable suspicion applies to a specific set of circumstances related to police searches. When a police officer wants to stop a suspect and conduct a brief search, the officer must have reasonable suspicion that a crime is being committed. Keep in mind that this type of search, commonly known as a 'stop and frisk', is very unobtrusive - it is limited to a search for weapons over the suspect's clothing.

The reasonable suspicion standard was first announced by the United States Supreme Court in the Terry v. Ohio case. The defendant in the case, John Terry, was stopped by an undercover police officer on the suspicion of pick-pocketing. The officer searched Terry and found a gun in his coat pocket. The Supreme Court determined that an officer may briefly stop and search a suspect for weapons if the officer has a reasonable belief that criminal activity is afoot.

Reasonable to believe

The reasonable to believe standard is another example of a pretrial, investigative standard of proof. This standard is applied to determine when an officer may search a suspect's vehicle after an arrest. Under this standard, an officer may search a suspect's vehicle after his arrest only if it's reasonable to believe that more evidence will be found in the vehicle.

The Supreme Court set forth the reasonable to believe standard in the Arizona v. Gant case. In that case, Rodney Gant was arrested for driving on a suspended license. The police searched his car and found drugs and weapons. The Supreme Court ruled that the search was proper because it was reasonable for the officers to believe that more evidence of a crime would be found in Gant's vehicle.

Probable cause

The probable cause standard of proof is most commonly applied to arrests and searches in criminal cases. In the context of a search for drugs or weapons, an officer must believe that there's a 'fair probability' that evidence of crime will be found during the search in order to satisfy the probable cause standard.

As for the standard required to effect an arrest, an officer must first believe there is a fair probability that a crime has been committed. While the so-called 'measurement' of what equates to a 'fair probability' varies, most jurisdictions agree that it is anywhere between a 30% and 40% probability.

Preponderance of the evidence

Under the preponderance of the evidence standard, the party making the claim will satisfy their burden if it's 'more likely than not' that the claim is true. Generally, this means that there's greater than a 50% chance that the party's assertion is correct.

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