Final answer:
Deceptive practices during interrogation are legal, but the use of threats of violence is not allowed and could make a confession inadmissible. The Fifth Amendment provides protections against self-incrimination, requiring that suspects are aware of their right to silence and to counsel during custodial interrogations.
Step-by-step explanation:
During a custodial interrogation, deception by law enforcement officers is not illegal and is indeed a common practice. However, the use of threats of violence, mild or otherwise, to elicit a confession is not permissible. According to the Miranda ruling, statements made as a result of custodial interrogation cannot be used in court unless procedural safeguards have been put in place to protect the suspect's self-incrimination rights under the Fifth Amendment. This includes being informed of the right to remain silent and the right to have counsel present during interrogations.
Additionally, tactics that amount to coercion, which could include threats of violence, can render a confession involuntary and therefore inadmissible in court. Police can use psychological strategies, such as suggesting they have evidence that they do not actually have, which is what occurred in the scenario with Prisoner A and Prisoner B. Nevertheless, police are prohibited from using false promises, torture, or threats, including those of violence, to derive confessions from suspects.