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What is Probable Cause?

In a nutshell, “probable cause” means a fact is “probably true.”

Many terms in Texas criminal law have specific definitions. “Probable cause” is not one of them. This standard of proof is lower than the proof standard in criminal trials but higher than the standard of evidence in civil trials. As an illustration, an Iowa federal judge recently ruled that officers had probable cause to pull over a man for traveling 66 in a 65, even though they knew those charges wouldn’t hold up in court. A RADAR gun has a margin of error of plus or minus 1 mph.

Because the burden of proof is so low, probable cause challenges are often difficult to win. However, to a determined Fort Worth criminal defense lawyer, the fight is worth fighting. There is a difference between “difficult to win” and “impossible to win.” Furthermore, if lawyers don’t stand up for individual rights, police officers will keep taking shortcuts and keep ignoring people’s rights. This process ends badly for everyone.


Search and arrest warrants must be based on probable cause affidavits. An affidavit is a sworn, official court document that is usually based on personal knowledge of the facts described in that affidavit.

Frequently, officers heavily rely on information provided by a confidential informant in search warrant affidavits. Many CIs receive tens of thousands of dollars for the information they provide. Others receive or hope to receive leniency in another proceeding. So, the CI receives love or money. Many people will say and do almost anything for love or money. Therefore, an affidavit that over-relies on a CI may lack probable cause.

Arrest warrants must be based on probable cause as well. Usually, the affiant (person who swears out the affidavit) provides details about the criminal investigation, which indicate that the defendant is “probably” guilty. Lack of personal knowledge could be an issue, especially in multi-agency investigations.

Incidentally, there is no statute of limitations on arrest or search warrants. Once authorities issue warrants, they are valid until a peace officer serves them, even if that service does not happen for years or decades.

On a related procedural note, grand juries must have probable cause to indict defendants. The grand jury indictment rate is over 99%, partially because the burden of proof is so low.

Additionally, grand jurors only hear one side of the story. A Fort Worth criminal defense attorney cannot challenge evidence, make legal arguments, or even be in the same room as the grand jurors.


A DUI investigation is a good example of the role of probably cause in an arrest. Initially, officers look for physical evidence of intoxication, like bloodshot eyes. They also typically ask drivers if they have been drinking. Many drivers respond with something like, “I only had a couple of beers,” even though they probably have a Constitutional right to remain silent at that point.

Physical symptoms and such admissions are not probable cause of intoxication. At best, they are only probable cause that the defendant has been drinking.

Instead, officers rely on the results of the Field Sobriety Tests, like the walking-a-straight-line test, to establish probable cause of intoxication, which in court means the loss of mental or physical faculties because of alcohol or substance use.

FST results often do not prove intoxication beyond a reasonable doubt. People could perform badly on these tests because they are sacred, nervous, sleepy, or clumsy. But the results establish probable cause of intoxication.

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