When a New York resident is being questioned by police, he or she is free to walk away as a formal arrest has not been made. However, once a police officer prevents a resident from walking away, he or she has been detained and is now under arrest. In order for an arrest to be legal, the officer must have had "probable cause".
Probable cause is defined as reasonable grounds for pressing a charge, searching a person or taking a person into custody. Essentially, probable cause prevents the authorities from rounding up those who could potentially be innocent simply because they may be deemed as a threat or as undesirable. Probable cause must be established through some sort of factual evidence or through observation. An officer may also have probable cause to take a person into custody based on his or her expertise and on circumstantial evidence as long as a crime has been committed. If probable cause is established, the authorities are protected against potential wrongful arrest lawsuits.
There is no rule regarding the amount of evidence needed to establish probable cause. In fact, the standard is designed to be flexible, which allows the judge to better balance law enforcement abilities to conduct investigations while protecting the rights of citizens.
Those who are taken into custody could potentially be found guilty of whatever crime they are accused of committing. A conviction on any criminal charge can have a major impact on a person's life. In some cases, for example, a person accused of theft could potentially face a jail sentence, probation and fines. If a person has been taken into custody, a criminal defense attorney could challenge the charges especially if the evidence against the accused person is weak or if the police did not have probable cause.