Probable cause is a requirement afforded by the Fourth Amendment. Before you can be arrested and charged with a crime, the arresting officer must have probable cause for doing so, which amounts to protection against unreasonable arrests, warrants, searches, or seizures. Probable cause can usually be established when there are reasonable grounds for believing that a crime was committed. Because the legal bar for probable cause is low, there is generally enough probable cause to proceed with a grand jury hearing.