Final answer:
The confession obtained by placing an informant in the defendant's cell would likely be inadmissible in court due to the violation of the suspect's rights. The suspect was not informed of their right to remain silent and not incriminate themselves. The confession was also obtained through coercion and trickery, rendering it involuntary.
Step-by-step explanation:
The confession obtained by placing an informant in the defendant's cell would likely be inadmissible in court due to the violation of the suspect's rights. According to the Fifth Amendment of the United States Constitution, a person has the right to remain silent and not be compelled to incriminate themselves. By placing an informant in the cell, the police knowingly elicited incriminating statements from the suspect without informing them of their rights. This violates the suspect's Fifth Amendment right against self-incrimination.
In addition, the police did not obtain a confession in a lawful and voluntary manner. The use of an informant to deliberately elicit information from the suspect can be considered a form of coercion or trickery, which can render the confession involuntary and therefore inadmissible in court.
Furthermore, the confession pertains to a separate case of voluntary manslaughter that is unrelated to the robbery charge. It is important to note that confessions must be obtained in a lawful manner, and the use of informants in cells is a controversial practice that can raise ethical and legal concerns.