The Fourth Amendment to the United States Constitution and Article 1, §9 of the Texas Constitution prohibit unreasonable searches and seizures by law enforcement officers. It is well established that the basic purpose of the Fourth Amendment is to safe guard the privacy and security of individuals against arbitrary invasion by governmental officials. Hayes v. State, 475 S.W.2d 739, 741 (Tex.Crim.App. 1971). The same is true of Article 1, §9 of the Texas Constitution. Kolb v. State, 532 S.W.2d 87, 89 (Tex.Crim.App. 1976).
There are three recognized categories of interactions between law enforcement officers and other individuals: (1) encounters, (2) investigative detentions, and (3) arrests.
An encounter is a friendly exchange of pleasantries or mutually useful information. In an encounter, a law enforcement officer is not require to possess any particular level of suspicion and the individual is free to walk away and not answer any questions asked by the law enforcement officer. Hawkins v. State, 758 S.W.2d 255, 259 (Tex.Crim.App. 1988).
An arrest occurs when an officer takes an individual into custody. A law enforcement officer must have probable cause to arrest an individual if there is no warrant to arrest that person. In order to establish probable cause for an arrest, the facts and circumstances within the officer’s knowledge and of which he had reasonably trustworthy information must be sufficient to warrant a prudent man in believing that the individual had committed or was committing a crime. Parker v. State, 206 S.W.3d 593, 596 (Tex.Crim.App. 2006).
The concept of investigative detentions originated with Terry v. Ohio, 392 U.S. 1, 88 S.Ct. 1868 (1968) which sought to ensure police action that fell technically short of an arrest was not immune from Fourth Amendment protection. In an investigative detention, also known as a Terry stop, the officer must have articulable facts that, in light of his experience and personal knowledge, together with inferences from those facts, would reasonable warrant the intrusion on the freedom of the individual stopped. Terry, 392 U.S. at 21. The officer must have a reasonable suspicion that some unusual activity is occurring or has occurred, and the person he has detained is connected with the activity and that the activity is related to the commission of a crime. Hoag v. State, 728 S.W.2d 375, 380 (Tex.Crim.App. 1987); Daniels v. State, 718 S.W.2d 702, 704 (Tex.Crim.App. 1986, en banc); Johnson v. State, 658 S.W.2d 623, 626 (Tex.Crim.App. 1983). An investigative detention is a seizure under which the individual is not free to leave. Francis v. State, 922 S.W.2d 176, 178 (Tex.Crim.App. 1996, en banc).
A traffic stop is a “seizure” within the meaning of the Fourth Amendment. United States v. Brigham, 382 F.3d 500, 506 (5th Cir. 2004, en banc). Because a routine traffic stop is more analogous to an investigative detention than a custodial arrest, traffic stops are analyzed as a Terry stop. Haas v. State, 172 S.W.3d 42, 50 (Tex.App. – Waco 2005, pet. ref’d.).
Therefore, for a traffic stop to be lawful in Texas, the officer must have a reasonable suspicion that some unusual activity is occurring or has occurred, and the person he has detained is connected with the activity and that the activity is related to the commission of a crime; the crime being a violation of the traffic laws of Texas.