No. The Miranda warning is only in effect during a custodial interrogation. This means that the person being questioned is in custody or in an environment in which the person does not believe that he is free to leave.
For example: Officer Jones is investigating a robbery at the local supermarket. The cashier indicates that a patron named Mary Smith may have seen the robber. When Officer Jones interviews Mary, Mary makes statements implicating herself in the robbery as a lookout. Can Mary`s statements be used against her later, even though she was not read her Miranda Warning? The answer is yes, because Mary was not in custody when she was being asked the questions. Therefore, Mary was free to leave if she wanted to.
