Final answer:
Once a suspect in the United States requests the presence of an attorney or invokes their right to remain silent, the police must immediately cease questioning.
Step-by-step explanation:
In the United States, the questioning of a suspect must immediately cease once the suspect invokes their right to remain silent or requests the presence of an attorney. This is based on the principles established in landmark court cases such as Miranda v. Arizona and Escobedo v. Illinois. The police must inform the suspect of their rights, including the right to remain silent and the right to an attorney, before questioning begins. If the suspect asserts these rights, the interrogation must stop.