Criminal procedure

Criminal procedure deals with the set of rules governing the series of proceedings through which the government enforces substantive criminal law. Municipalities, states, and the federal government each have their own criminal codes, defining types of conduct that constitute crimes. Title 18 of the U.S. Code outlines all federal crimes. Typically, federal crimes deal with activities that either extend beyond state boundaries or directly impact federal interests.

The U.S. Supreme Court, pursuant to its authority under the Rules Enabling Act, first promulgated the Federal Rules of Criminal Procedure, (F.R.Crim.Pro.) which Congress, in turn, passed. The Federal Rules outline the procedure for conducting federal criminal trials. Similarly, states have their own codes of criminal procedure of which many closely model the Federal Rules. The Federal Rules incorporate and expound upon all guarantees included within the U.S. Constitution's Bill of Rights. A few of the rights guaranteed to criminal defendants by the Constitution include the guarantees of due process and equal protection under the laws, the right to have legal counsel present, the right to confront witnesses, the right to a jury trial, and the right to not testify against oneself. While state constitutions and procedural rules may increase the protection afforded to criminal defendants, they may not offer less protection than that guaranteed by the U.S. Constitution.

Investigatory and Accusatory Police Procedure

The U.S. Constitution, the Federal Rules and the federal court system's interpretations of both provide guidance and procedural canons that law enforcement must follow. Failure to follow such procedure may result in the suppression of evidence or the release of an arrested suspect.

Substantive due process requires police to make criminal defendants aware of their rights prior to the defendant making any statements if the government intends to use those statements as evidence against the defendant. For example, law enforcement must ensure that the defendant understands the right to remain silent and the right to have an attorney present, as the Fifth and Sixth Amendments respectively provide. The defendant must knowingly, intelligently, and voluntarily waive those rights in order for the government to use any statements as evidence against the defendant. See Miranda v. Arizona, 384 U.S. 436 (1966).

Law enforcement also must abide by the confines of the Fourth Amendment, which prohibits the government from performing unreasonable searches and seizures. Courts ordinarily suppress evidence obtained during an unreasonable search or seizure and offered against the accused. See Mapp v. Ohio, 367 U.S. 643 (1961).

In order to avoid illegally searching or seizing the property of a suspect, law enforcement personnel typically obtain search warrants. To obtain a search warrant, law enforcement must show probable cause, must support the showing by oath or affirmation, and must describe in particularity the place they will search and the items they will seize. A judge can find probable cause only be examining the totality of the circumstances. Exceptions to the warrant requirement exist, however. These exceptions include searches made at or near the border; a search following a lawful arrest; a stop-and-frisk arrest; where the seized items are in plain view; where the articles are in an automobile; where the private individual makes the search; and under exigent circumstances, where the officer has probable cause for a search to find a crime or evidence relating to a crime.

The Fourteenth Amendment of the U.S. Constitution applies all substantive due process rights to state criminal defendants.