In a criminal case, the accused must be proved guilty by the district attorney; however, the word 'prove' has several different meanings in a legal sense. Courts and law established over hundreds of years has actually divided 'proof' into categories, ranging from a low level of proof to overwhelming proof. Each level of proof is used in a different way during the criminal justice system, and will be explained below.
A Reasonable Suspicion is generally the lowest level of proof needed in a criminal case. Common uses are when an officer observed suspicious behavior not amounting to anything illegal, the officer may stop or shortly detain the suspicious individual, if the officer has a reasonable suspicion there is something illegal going on. Concrete proof of illegal conduct or a crime is not needed at this point; just a suspicion that is reasonable in light of the circumstances. In the above example, a reasonable suspicion detention can lead to a pat down frisk for weapons, and in some cases, may yield drugs or other illegal items that can lead to arrest.
Probable Cause means there is evidence of guilt that is more than a mere reasonable suspicion, but not enough to convict at trial. Probable cause is typically used in two major ways in a criminal case. First, to make an arrest, an officer must have probable cause, that is, an officer must have evidence that the accused probably commit the crime. Probable Cause is also used by Judges when authorizing search or arrest warrants. Judges or magistrates will look at the written affidavit of a sworn officer, and examine the evidence presented in it to ensure the information and proof rises to the level of Probable Cause. If the evidence does not show probable cause, the judge is supposed to reject the warrant application. Lastly, Judges review the evidence for probable cause when hearing information on felony cases, to ensure there is enough proof to hold a person for trial on a felony.
Clear and Convincing
Clear and Convincing evidence is more commonly used in civil cases, but the courts still apply the legal standard at certain motions to suppress or other motions for trial. Clear and Convincing evidence tends to mean proof that is more likely than not. Some people quote 51%, although the evidence is rarely put into percentiles in practical use. Clear and convincing generally means the evidence of guilt is a hair more than the evidence against guilt.
Beyond a Reasonable Doubt
Beyond a Reasonable Doubt is the standard of proof needed at trial in order to convict a defendant. Beyond a reasonable doubt sounds vague, and there is no percent to put to the level of proof -- instead, typically jurors in a jury trial are asked to weigh and evaluate the evidence before them. At the end of the trial, after hearing all of the evidence, the jury will decide if the evidence has proven guilt beyond a reasonable doubt, or if the evidence was lacking in some way, and therefore did not prove guilt beyond a reasonable doubt. Beyond a Reasonable Doubt is based on the fact that few things are 100%, but knowing that and considering only reasonable conclusions and reasonable evidence, did that evidence prove guilt enough to satisfy all reasonable questions or doubts of the defendant being not guilty.