Arrest Warrants and Probable Cause
All arrest warrants begin with the demonstration of what is called probable cause. This term is taken from the Fourth Amendment to the U.S. Constitution, and is included in the constitutions of individual states as well. Over the years, probable cause has been defined to constitute known facts that lead to the reasonable expectation that evidence of a crime exists or will be found. In other words, probable cause means more than just a general suspicion. It must be fact based and specific to an individual. The standards of probable cause are an important issue in law enforcement and the issuance of arrest warrants, because an arrest initiates a proscribed legal process that moves toward a criminal trial according to timelines and rules in state laws.
Probable Cause Hearings
Only courts and judges--and others they may invest with the power--can issue an arrest warrant. The process usually involves the attorney general of a state going before a judge or court and offering evidence of probable cause. This most often occurs after police or another law enforcement agency has conducted an initial investigation or otherwise obtained evidence implicating someone in a specific criminal act. A private citizen who has such evidence might be asked to appear at a probable cause hearing or submit a sworn affidavit. If the police refuse to prosecute someone on the basis of a private individual's probable cause evidence, they can go before a judge themselves. If the evidence is later found to be untrue, however, they can be liable for perjury. A person about whom a probable cause hearing is being conducted has no rights to be present or represented by legal counsel. A probable cause hearing is not a trial and does not decide a person's guilt. It's merely a procedural step that allows a person to be detained lawfully by the police. Whereas a person who is found not guilty at a criminal trial can never be tried again for the same crime, a court's rejection of probable cause doesn't preclude future attempts to obtain a warrant for the same crime--even for the same evidence--before other courts.
In the past, arrest warrants were paper documents that had to be processed and eventually entered into a computer database before they were widely accessible by law enforcement agencies across the country. Even then, there was a chance that errors could be made or that changes in the warrant might not be reflected correctly in all databases. Today, clerks of the court can enter warrants electronically directly into statewide and national databases that are immediately accessible throughout the country. This increases the speed at which arrest warrants can be acted upon and reduces the chances of error.