Once someone detained by the police invokes Miranda by expressing a desire to remain silent, have counsel present, or both, the police must stop interrogation. (See Miranda Rights: Cutting Off Police Questioning.) But this isn't necessarily the end of the story: Some circumstances allow the prosecution to use statements a suspect makes after having invoked Miranda. These circumstances constitute a waiver of Miranda rights. (Sometimes prosecutors can use even statements obtained in violation of Miranda.)
Courts understand that interrogation is inherently coercive and that there's a difference between freely choosing to initiate or participate in a conversation and feeling compelled or manipulated into it. Therefore, a defendant must have a chance to understand the Miranda rights and must choose to waive them for a waiver to be valid.
There's no time limit for invoking Miranda rights. After receiving the warnings, a detainee may invoke the rights immediately or after answering some questions. Whenever that invocation occurs, the police must stop investigative questioning. But any statements preceding assertion of Miranda rights are likely to be admissible.
(Sometimes police officers will question a suspect once without the Miranda warning, then interrogate again with it. To learn about this tactic—and its legality—see Mid-Interrogation Miranda Warnings.)
Generally, the police must immediately stop probing if the detainee invokes either the right to remain silent or the right to counsel. If the suspect invokes the latter, questioning must cease until counsel is available. But if the detainee invokes only the right to remain silent, the police may reinitiate questioning at a later time, provided that they honor the right to remain silent.
What it means to "honor" the right to remain silent after a suspect invokes it isn't always entirely clear. Courts consider the circumstances of renewed questioning, including the passage of time, whether the police gave fresh Miranda warnings, and whether they asked questions about a different crime.
For example, suppose the police arrest George as a suspect in some robberies. They stop questioning him about the robberies immediately after he asserts his right to remain silent. However, two hours later, a different officer Mirandizes him again and begins asking him questions about an unrelated murder. George doesn't reassert his right to remain silent. Any statements he makes are presumptively admissible in court. (Michigan v. Mosley, 423 U.S. 96 (1975).)
A defendant's statements after asserting Miranda may also be admissible if he or she initiates the conversation. But that's only if the police give a fresh set Miranda of warnings once the discussion picks up.
For example, assume officers take John into custody and give him the Miranda warnings. He tells them that he wants to remain silent and wants counsel present. But after a few minutes of riding in the squad car in silence, he starts to talk about what happened. The police give him the Miranda warnings again and then ask him questions. Any statements John gives after the second set of Miranda warnings will probably be admissible in court.
If a detainee invokes the right to counsel for only a limited purpose, the police may interrogate "around" that purpose. For example, suppose that, after being Mirandized, Becky doesn't claim her Miranda rights and answers questions. The interrogating officer asks her to sign a written statement, but she says that she wants counsel to read it over first.
Becky has invoked her right to counsel for the limited purpose of reviewing the statement—she hasn't invoked it generally. Thus, although the police must wait for her lawyer to be present to persist with the signature request, they may continue questioning her for as long as she is willing to speak with them.
A suspect's assertion of the right to counsel ceases to apply if there is a break in incarceration. The assertion of the right doesn't carry over to the next detention. For example, assume Glen invokes his right to counsel and is released from custody. Officers later pick him up again: They're free to question him after re-Mirandizing him. It's up to Glen to reassert his right to counsel.
There has been a break in custody only if the detainee has been removed from the pressures of custodial interrogation for a significant period of time. If Glen invokes his right to counsel while captive in jail and officers return several hours later and begin questioning him again, while he is still in jail, then they have violated Miranda. However, suppose Glen has been serving time in prison when officers first approach him. They take him out of the general prison population, to the local jail, where they question him. He invokes his right to counsel. They return him to the general prison population. Fourteen days after returning him to the general prison population, they take him to the local jail again to question him again. They Mirandize him and he agrees to speak. His statements are likely admissible. (Maryland v. Shatzer, 559 U.S. 98 (2010).)
Most lawyers would advise anyone who could be a suspect not to speak to the police until having spoken with counsel. Anyone who's in trouble with the law, whether having already given up incriminating information or not, should consult an experienced criminal defense attorney. The law on issues like the rights to silence and counsel can vary from one state to another. A lawyer will be able to explain the law and how it applies to your situation.