Any evidence or statements made by a person prior to their arrest may be used against them if the officer had reasonable suspicion supporting their decision to perform the detention. Once a person has been arrested, any statements made as a result of custodial interrogation cannot be used against them unless they have been informed of their Miranda rights, which is the right to remain silent. There is a concept called res gestae, which is a Latin term which basically means that something happens contemporaneously or part of the arrest. Statements made at the time of an arrest or as a result of an arrest may be admissible against a person even if they haven’t been informed of their right to remain silent. The distinction here is that once a person is in custody, statements cannot be used against them if those statements were the result of custodial interrogation and if the person was not informed of their right to remain silent.
In a DWI arrest, a person is typically pulled over, investigated, and asked to perform field sobriety tests. They might be placed under arrest and not informed of their right to remain silent. Under such circumstances, many people will think that since they weren’t informed of their right to remain silent, everything will be thrown out. This, however, is not necessarily true. The police will typically take a person to the police department, ask them to submit to a breath or blood test, and then inform the person of their right to remain silent before going through a list of carefully prepared questions that essentially reads like a script. At that point, they are interrogating the person and must inform that person of their right to remain silent in order to use any of the information they obtain.
Detectives and patrol officers are trained to interrogate people in a manner that will get them to make incriminating statements. Detectives undergo further training to use psychological ploys and methods for obtaining incriminating statements. They typically ingratiate themselves to that person, make the person feel comfortable, and create the impression that they are there to help. In fact, they might even lie to the person or appeal to their conscience. They are very well-trained at asking questions from different perspectives in ways that call for certain incriminating answers.
The police are allowed to lie to people.
A frequently used tactic by the police is to tell someone that they will “go easy” on someone if they cooperate. In reality, “going easy on someone” is not even an option for a police officer; they have a duty to investigate crimes, and once they have completed their investigation, they must turn over the information to the prosecutor or district attorney. At that point, it is the district attorney’s place to decide how vigorously to prosecute the defendant and whether or not to “go easy” on them.