A criminal suspect's lawyer is only doing his job when he calls you during your investigation or after his client's arrest and "instructs" you not to discuss the case with his client unless the lawyer is present. That doesn't mean, however, that you have to follow the attorney's instruction.
The Constitution does not forbid you to talk to a person just because that person has an attorney, or just because the attorney tells you not to do it. Instead, the law focuses on whether the suspect is willing to talk without his or her attorney present. Although this is a well established principle dating back at least a quarter of a century, some officers and attorneys (and some judges) still experience uncertainty and nervousness about police interrogation of a represented suspect.
The U.S. Supreme Court has been very clear, however, in setting forth the constitutional rules.
Moran v. Burbine
In Providence, Rhode Island, Brian K. Burbine beat a woman to death with a metal pipe. Providence officers had no suspect until Burbine was arrested in nearby Cranston for a breaking and entering, and an informant gave police a tip that Burbine had committed the Providence murder.
Burbine's sister learned that her brother had been arrested, and she called a public defender. The public defender phoned the Cranston station, said that she represented Burbine, and instructed police not to talk to him until she arrived at the station. She was told that there were no plans to put Burbine in a lineup or question him about the burglary.
Police did not tell the lawyer that Burbine was suspected in the Providence murder, or that he was about to be questioned in that case. They also did not tell Burbine a lawyer had phoned on his behalf. Instead, Providence officers gave Burbine a Miranda warning, obtained his waiver, and conducted an interrogation, during which he confessed to the killing.
At trial, Burbine moved to suppress his confession on various grounds. His motion was denied and he was convicted. On appeal, the First Circuit of the U.S. Court of Appeals reversed, ruling that Burbine's waiver was invalidated by police deception of the attorney and her client. The state appealed to the Supreme Court, which affirmed the conviction.
At the Supreme Court, Burbine first repeated his arguments that his Miranda waiver was invalid because he had not been told of the attorney's phone call, and because she had not been told of his pending interrogation about the murder. The court rejected these arguments in its 1986 opinion, ruling as follows:
"We have no doubt that defendant validly waived his right to remain silent and to the presence of counsel. Events occurring outside the presence of the suspect and entirely unknown to him surely can have no bearing on the capacity to comprehend and knowingly relinquish a constitutional right.
"Once it is determined that a suspect's decision not to rely on his rights was uncoerced, that he at all times knew he could stand mute and request a lawyer, and that he was aware of the state's intention to use his statements to secure a conviction, the analysis is complete and the waiver is valid as a matter of law.
"The state of mind of the police [being aware of his lawyer's wishes] is irrelevant to the question of the intelligence and voluntariness of defendant's election to abandon his rights. Nor are we prepared to adopt a rule requiring that the police inform a suspect of an attorney's efforts to reach him.
"Because defendant's voluntary decision to speak was made with full awareness and comprehension of all the information Miranda requires the police to convey, the waivers were valid."