Probable cause isn't necessarily needed to conduct a traffic stop. There's a few legal reasons for a cop to conduct a stop.If you have been arrested or charged with a crime, you have rights. Read this article to learn more. A person's prior conviction, arrest or even suspect records could be used as probable cause for an investigation or arrest. Probable cause means law enforcement must show evidence that it's more likely than not that evidence of a crime will be found in the place they want to search. If a police officer sees someone committing a crime, they can arrest that person without a warrant. The prosecuting attorney can issue a charge if the prosecutor believes that "probable cause" exists that the suspect committed the offense. Probable cause means that there is a reasonable belief, based on facts, that you have committed a crime. For an arrest to be lawful, the arresting officer must have probable cause to believe the driver committed an offense.