Ideally, arrests should be made only after probable cause has been proven and a warrant has been issued by a magistrate who impartially considered all the relevant facts. Instead, warrantless arrests are the rule. Many police officers have never even had the experience of asking for a warrant.
Police are not supposed to arrest anyone unless they have a warrant, but there are countless exceptions. The exceptions have all but made getting a warrant obsolete. Generally, police may arrest those who commit a crime in the presence of the officer.
Texas Courts have ruled it is legal for police officers to approach any person to simply talk, if the officer has a right to be there. Technically, people are free to ignore the officer and walk away from him. Common sense tells us that almost no one feels free to walk away from such an encounter, but that’s the law. No “seizure” occurs in this scenario.
“Seizure” of a person occurs, however, when the police officer temporarily “detains” someone. Detention is allowed if the officer has “reasonable suspicion” that some unusual activity is happening, that the unusual activity is related to a crime, and that the person detained is somehow connected to the unusual activity. This is called a “temporary detention”, and it may last only as long as the circumstances justify it. In other words, the moment the officer learns that his suspicion is incorrect, detaining the person any longer is illegal.
For example, a police officer sees a man with a ski mask in 90-degree weather running from the direction of a bank which has alarms sounding. The officer has reasonable suspicion to temporarily detain the man.
“Probable Cause” is the standard used to determine whether the police officer has sufficient reason to arrest a person. Basically, that means the officer has good reason to arrest when the facts he knows are enough to allow a reasonable man to form a belief that the person detained has actually committed a crime.
*All answers are for people 21 years or older, do not involve enhancements, are not exclusive, and are limited to Texas.