Anyone who has spent much time with pop culture portrayals of lawyers and police officers -- whether it is in books, movies or on television -- has probably heard the term "probable cause." Initially, at least as far as the law of the United States is concerned, it appeared in the Fourth Amendment of the United States Constitution. The Fourth Amendment, a cornerstone of criminal defense in the U.S., protects people against "unreasonable searches and seizures" unless there exists "probable cause."
Many states, including Texas, adopted the Fourth Amendment's probable cause requirement in their own state constitutions. Article One, section nine of the Texas constitution also requires probable cause for a search or seizure to be valid in the state. The United States Supreme Court and the state courts of Texas have interpreted these constitutional clauses to mean that all warrantless searches or seizures -- including arrests and detentions -- of people or property are presumed invalid, unless it can be proven that the law enforcement officer had probable cause to do so.
A search or arrest warrant also requires a showing of probable cause "supported by oath or affirmation" before it will be issued. The question of what constitutes probable cause, however, is not always an easy one and has changed over the centuries. An entire body of law has, thus, developed around Fourth Amendment searches and seizures.
As it stands in Texas, probable cause is a combination of facts and circumstances that would lead a reasonable law enforcement officer to believe that a crime had been committed or would be committed. If an officer is in a legal position to directly observe these facts and circumstances, the can make an arrest, perform a search or apply for a warrant to do either or both. Because probable cause is an important element in any arrest -- from a DWI to a drug charge -- anyone detained or arrested for a crime in Texas should make sure they understand their Fourth Amendment rights.