OPINION OF THE COURT
GIBBONS, Circuit Judge.This is an appeal by the United States pursuant to 18 U.S.C. § 3731 from an order of the district court granting the motion of defendant, Lloyd Eugene Crook, to quash an incriminating statement which he gave to agents of the Federal Bureau of Investigation on January *137917, 1973. Crook is before the district court on an indictment charging robbery of a Wyncote, Pennsylvania bank, and the challenged statement. admitted that he did so. The motion to suppress asserted (1) that the F.B.I. should have called Crook’s attorney before they interrogated him, and (2) that his mental condition was such on January 17, 1973 that he could not appreciate the significance of the Miranda warnings given him and thus his waiver of Miranda rights was not voluntary. The district court held a hearing in which psychiatric evidence as to Crook’s mental condition was presented, and concluded:
“If the mental capacity of the defendant was the sole issue in this case I would hold that his mental capacity was such that there was no violation of his rights in obtaining the statement because of any mental condition arising out of any mental illness that the defendant may have had at that time, or of any mental incapacity, and I would hold, if that were the sole issue in this case, that the Government has met its burden of proof that the statement was validly obtained.” Appendix at 90.
The court held, however, that the statement should be suppressed because the interrogation was in violation of Mas-siah v. United States, 377 U.S. 201, 84 S.Ct. 1199, 12 L.Ed.2d 246 (1964). That holding is inconsistent with decisions of the Supreme Court and this court, and we reverse.
I. THE MASSIAH ISSUE
On January 17, 1973, Crook was arrested in Peoria, Illinois pursuant to a warrant charging him with robbery of the Wyncote, Pennsylvania bank on December 22, 1970. He was taken to the Peoria F.B.I. office where a standard written advice of rights form was given to him. He read and signed this form which was witnessed by two F.B.I. agents. The form was not read to him. It contains all the warnings required by Miranda, and above the signature line appears the language:
“I have read this statement of my rights and I understand what my rights are. I am willing to make á statement and answer questions. I do not want a lawyer at this time. I understand and know what I am doing: No promises or threats have been made to me and no pressure or coercion of any kind has been used against me.”
Appendix at 52. (emphasis added). Crook was then asked if he committed the Wyncote robbery and he denied it. One of the agents told him that his sister had identified him as the person in the Wyncote bank surveillance photographs. He then responded “Well if you say its me, its me.” Crook then answered specific questions which were reduced to a narrative confession which he signed.
At the time of the interrogation Crook was awaiting sentence on an attempted bank robbery charge in Peoria, Illinois. Arrested on that charge on December 18, 1972, he had later been arraigned and Randall Moon, a Peoria attorney, had been appointed to represent him. Through Mr. Moon he had tendered a guilty plea on the Peoria charge on the basis of a recommendation by the government of a three-year probationary sentence. On January 17, 1973 the Peoria judge had not yet finalized this plea bargain by accepting the guilty plea. One of the F.B.I. agents who arrested Crook on the Wyncote charge was the case agent on the Peoria case and was aware that Mr. Moon represented him in that case. That agent was present during the January 17, 1973 interrogation. Following the execution of the signed statement, an attempt was made to call Mr. Moon, but he was not in his office. On the basis of the foregoing facts, which are essentially undisputed, the court ruled:
“Clearly in this case the counsel representing the defendant in the Peoria bank robbery had an interest to protect in that pending proceeding. I would point out, however, that there is no contention and no evidence that the defendant was actively prevented *1380from contacting Mr. Moon, or that the statement was obtained by any type of physical or mental coercion in the classic meaning of the word.
I do not find in this case, considering the totality of all the circumstances, that the Government has met its burden to prove that the statement was properly obtained, and that the defendant and the accused did voluntarily intelligently and knowingly waive his right to counsel.” Appendix at 99-100.
The totality of the circumstances is that Crook, whom the court found to be competent, uncoerced and unrestrained from calling an attorney, signed a waiver stating “I do not want a lawyer at this time,” but that the agents knew he was represented by a lawyer in connection with another totally unrelated offense. The only additional factor to which the district court referred was the fact that the Peoria attorney had an interest to protect in that pending proceeding. Undoubtedly that interest was in having the Peoria court accede to the plea bargain. That factor is irrelevant to the admissibility of the statement in this proceeding in which the issue is the volun-tariness of the Miranda waiver. Whether or not the interrogator knew the defendant had counsel in an unrelated case at the time of the waiver has nothing to do with whether the waiver was knowing and intelligent, so long as the defendant knew he had counsel. The relevant inquiry is not what the F.B.I. agent knew but what Crook knew and understood. No contention has been made that Crook was unaware, when he signed the waiver, that Moon represented him in connection with the Peoria case. The finding that the government has not proved that the statement was properly obtained after a valid Miranda waiver, resting as it does on the single factor that the F.B.I. agent knew Crook was represented by an attorney in an unrelated case, is clearly erroneous.
We are urged, however, that as a matter of law any interrogation by government agents of a defendant whom they know to be represented by an attorney, even in another case, is unlawful under Massiah v. United States, supra. The Supreme Court rejected such a rule in Hoffa v. United States, 385 U.S. 293, 309-310, 87 S.Ct. 408, 17 L.Ed.2d 374 (1966), and we recently followed Hoffa in United States v. Osser, 483 F.2d 727, 733-734 (3d Cir.), cert. denied, 414 U.S. 1028, 94 S.Ct. 457, 38 L.Ed.2d 321 (1973).
These additional observations of the district court are worthy of note:
“But I fail to see what good written opinions condemning certain police procedures are if they do not prevent repetition.
I hope that it will have a prophylactic effect as to future interrogations.” Appendix at 98.
These observations suggest that the district court looks upon any interrogation of a defendant represented by an attorney as unethical in the absence of the attorney’s consent, and that the sanction for such an ethical violation is suppression. See United States v. Thomas, 474 F.2d 110, 112 (10th Cir.), cert. denied, 412 U.S. 932, 93 S.Ct. 2758, 37 L.Ed.2d 160 (1973); A.B.A., Code of Professional Responsibility, DR 7-104(A)(l) (1969). We share the district court’s unease with the practice of talking to a represented defendant behind his attorney’s back. See, e. g., United States v. Cobbs, 481 F.2d 196, 200 (3d Cir.), cert. denied, 414 U.S. 980, 94 S.Ct. 298, 38 L.Ed.2d 204 (1973). But the Code of Professional Responsibility, assuming it should guide the conduct of F.B.I. agents as well as United States attorneys, can be enforced by sanctions only under our supervisory powers. See United States v. Springer, 460 F.2d 1344, 1354 (7th Cir.), cert. denied, 409 U.S. 873, 93 S.Ct. 205, 34 L.Ed.2d 125 (1972). Those powers are subject to the control of Congress. In the Omnibus Crime Control and Safe Streets Act of 1968, Pub.L. No. 90-351, tit. II, § 701, 82 Stat. 197, 211, Congress provided that “[i]f the trial judge de*1381termines that the confession was voluntarily made it shall be admitted in evidence . . . 18 U.S.C. § 3501(a). Presumably the constitutionally mandated requirements of the Miranda decision survive that enactment. See United States v. Marrero, 450 F.2d 373, 379 (2d Cir. 1971) (Friendly, J., concurring), cert. denied, 405 U.S. 933, 92 S.Ct. 991, 30 L.Ed.2d 808 (1972); C. Wright, 1 Federal Practice and Procedure § 76, at 121-22 (1969). We cannot, however, in exercising merely supervisory powers, disregard the congressional mandate of 18 U.S.C. § 3501(a). Since there was full compliance with Miranda, and hence with the fifth and sixth amendments, the district court is bound, in determining admissibility, by 18 U.S.C. § 3501(a). The statement should not have been suppressed for the reasons on which the district court relied.
II. THE COMPETENCY ISSUE
Crook urges that the order should nevertheless be affirmed because the district court erred in determining that he was competent, on January 17, 1973, knowingly and intelligently to make a Miranda waiver. See Collins v. Brierly, 492 F.2d 735 (3d Cir. 1974) (en banc). The court heard the testimony of three psychiatrists: Dr. Heller, who was court appointed, Dr. Thrasher, who was employed by the government, and Dr. Berman, for the defendant. All three agreed that Crook suffered from some form of mild chronic schizophrenia undifferentiated type. Their opinions as to his competency to make a valid Miranda waiver conflicted to some extent. We have independently examined the evidence as to Crook’s mental condition. See, e. g., Blackburn v. Alabama, 361 U.S. 199, 205 n. 5, 80 S.Ct. 274, 4 L.Ed.2d 242 (1960), and cases cited therein. We cannot say that the district court erred in concluding that the government met its burden of establishing a knowing and intelligent waiver. Thus we cannot affirm the suppression motion on that ground. Our conclusion that we cannot affirm on that ground, resting as it does on the superior opportunity of the trial judge to observe the witnesses, does not preclude a renewal of Crook’s competency contention at or before final hearing.
The order suppressing Crook’s statement of January 17, 1973, will be reversed.