(dissenting):
Appellant was convicted of violations of the narcotics laws. He first contends that his conviction should be reversed because the two-month and five-day delay between the date of the alleged sale and his arrest was unreasonable and prejudiced his defense. A review of the testimony at trial demonstrates, however, that the Government’s case was not “of such slender dimensions” as to require reversal of the conviction. The corroboration of the undercover agent’s identification of appellant by another witness to the transaction and the relative shortness of the delay lead to the conclusion that the police conduct in this case was reasonable.1 Nor was appellant’s claim of prejudice as strong as that in Ross v. United States, supra note 1. The risk of conviction of an innocent person — the basic concern of the Narcotics Delay cases 2 — was no greater here than in the ordinary criminal case.
Appellant’s second argument is based on the following occurrence. During the voir dire examination, trial counsel for appellant asked the prospective jurors:
“Are any of you or do you have close relatives who are connected with the Treasury Department or the Internal Revenue Service ?”
*591There was no response to this question. After trial, counsel for appellant discovered that one of the jurors was employed by the Treasury Department, apparently as a check numberer. The trial court, after hearing oral argument, denied appellant’s motion for a new trial based on the juror’s failure to answer this question.
The function of voir dire is to implement the constitutional guarantee of an impartial jury, a fundamental right of our system of criminal justice. To this end, the trial court is charged with the duty of striking jurors for cause.3 In addition, Congress has provided by rule and statute for peremptory challenges so that the parties may further insure an impartial jury; even when no actual bias appears, a juror may be struck because counsel, with or without reason, distrusts him. But neither judge nor counsel can do his part in securing an impartial jury, if a juror fails to respond truthfully to questions on voir dire. The question then arises under what circumstances is a false or misleading answer so significant as to require a new trial.
The case law has established three basic criteria to guide the trial court in ruling on motions for new trial based on improper responses at voir dire. First, if it is shown that the juror was biased against the losing party, a new trial is always required. No specific prejudice need be proved once it is clear that the constitutional guarantee of an impartial jury was violated.4 Second, if it appears that the nondisclosure “resulted from a purposefully incorrect answer or from deliberate concealment,” a new trial must be granted.5 Since the juror has violated his oath and impaired the statutory right of peremptory challenge, the materiality of the withheld information is usually considered irrelevant. Finally, if the nondisclosure was innocent, the trial court has some discretion in deciding whether to order a new trial. Its judgment, however, should be based upon a consideration of the reasons for the juror’s failure to disclose6 and of the materiality of the undisclosed information.7
It is impossible to apply these three criteria in this case because no evidentia-ry hearing was held to determine the details of the withheld information or *592the reasons for the juror’s false response.8 I think the trial court erred by not ordering this inquiry.9 Appellant’s motion for a new trial sufficiently revealed the necessity for such a hearing. He not only alleged a failure to respond by the juror, but he offered to prove the charge by documentary evidence. If more detailed allegations were required, the challenging party would have to conduct an extensive, and undesirable, private investigation, which would include questioning the juror out of court. Courts have generally been reluctant to authorize such practices.10 In the context of this case the practice would raise a substantial danger of “browbeating” potential witnesses, of refusals to cooperate by those witnesses, and of more false responses by the suspect juror. I think it preferable that the inquiry be conducted in open court where all parties can be represented. This procedure is more orderly and should, in the long run, best serve discovery of the truth.
The majority’s reliance on Spivey v. United States, 109 F.2d 181 (5th Cir. 1940) and Frazier v. United States, 335 U.S. 497, 69 S.Ct. 201 (1948) indicates that the judgment is affirmed solely on the ground that appellant’s trial counsel failed to exercise due diligence in discovering the falsity of the response. But on the motion for new trial the court told defense counsel:
“J think that you have been diligent in the interest of your client. I think that the alertness with which you filed this motion and [which you} demonstrated during the actual trial * * * shows that you have been diligent in his interest.” [Emphasis added.]
The force of this statement was weakened but not destroyed by a later observation of the trial court.11 The majority seems to explain this exchange by speculating on the mental processes of the trial court. I think this speculation is not sufficiently supported in the record and unduly minimizes the effect of the trial court’s statement that defense counsel was diligent.
Appellant, moreover, alleges that his trial counsel was completely occupied immediately before trial in arguing a motion for dismissal of the indictment. In addition, it is not clear how long before *593trial defense counsel received the jury-lists which stated the occupations of the prospective jurors. Resolution of these facts relating to diligence is within the peculiar competence of the trial judge who participated in the proceedings. This court should not undertake to make such findings of fact from an ambiguous and incomplete record.
I would remand the case to the District Court for reconsideration of the motion for new trial after an evidentiary-hearing on all the circumstances surrounding the juror’s failure to answer the question on voir dire, including a reexamination of the issue of diligence.
. See, e. g., Ross v. United States, 121 U.S. App.D.C. 233, 235, 349 F.2d 210, 212-13 (1965); Bey v. United States, 121 U.S.App.D.C. 237, 350 F.2d 467 (1965).
. See, e.g., Salley v. United States, 122 U.S.App.D.C. -, 353 F.2d 897, 898 (Nov. 24, 1965); Cannady v. United States, 122 U.S.App.D.C. -, -, 351 F.2d 817, 818 (1965).
. Disqualification for cause may be based on either of two separate types of bias. The first is where the juror is aware of and admits a feeling of bias. The second, and more common, finding occurs when the judge makes a pragmatic judgment that the juror’s relationship to the case is such that there is a substantial possibility of his unconsciously favoring one side or the other. See, e. g., Frazier v. United States, 335 U.S. 497, 510 n. 19, 69 S.Ct. 201 (1948); The Jury System in the Federal Courts, 26 F.R.D. 409, 466 (1960).
. E. g., Ryan v. United States, 89 U.S.App.D.C. 328, 331-332, 191 F.2d 779, 782-783 (1951); Carpenter v. United States, 69 App.D.C. 306, 307, 100 F.2d 716, 717 (1938); Consolidated Gas & Equip. Co. v. Carver, 257 F.2d 111, 115-116 (10th Cir. 1958). Cf., D.C.Code § 23-108 (1961). Stated alternatively, the rule is that a new trial must be granted where the undisclosed facts are such that, had they been known, a failure to dismiss the juror for cause would have been an abuse of discretion requiring a new trial.
. Ryan v. United States, supra note 4, 89 U.S.App.D.C. at 331, 191 F.2d at 782; Carpenter v. United States, supra note 4, 69 App.D.C. at 307, 100 F.2d at 717. See also Orenberg v. Thecker, 79 U.S. App.D.C. 149, 143 F.2d 375 (1944).
. For example: whether the questions were framed too technically to be understood, or whether the juror misunderstood the question or wrongly interpreted it. See, e. g., Orenberg v. Thecker, supra note 5.
. See, e. g., cases cited in notes 4 and 5 supra; Photostat Corp. v. Ball, 338 F.2d 783 (10th Cir. 1964). Two basic tests have evolved to measure the materiality of the nondisclosure. The first is whether the trial judge would have excused the juror out of an abundance of caution had the information been revealed on voir dire. The second is whether, in the opinion of the court, disclosure of the information would have resulted in a peremptory challenge to the juror.
. While it is unlikely that the juror possessed a subjective bias against appellant, it is possible that a complete examination of the nature of her employment and its relationship to the Narcotics Bureau of the Treasury Department would reveal professional or social ties to those charged with the enforcement of the narcotics laws. Under some circumstances these ties might require or permit a finding of bias. See note 3 supra. Alternatively, a finding of deliberate concealment would not be impossible, especially in view of the simplicity of the question which the juror failed to answer properly. Finally, until all the facts are known, it is impossible to measure accurately the materiality of the withheld information.
. The Supreme Court has repeatedly emphasized the duty of the court to be particularly
“ * * * solicitous to discover whether * * * [the juror’s governmental], employment, or * * * the relation of the particular governmental activity to the matters involved in the prosecution * * * [resulted in] actual bias * * United States v. Wood, 299 U.S. 123, 134, 57 S.Ct. 177, 180, 81 L.Ed. 78 (1936).
See also, Dennis v. United States, 339 U.S. 162, 168, 70 S.Ct. 519, 94 L.Ed. 734 (1950); Frazier v. United States, 335 U.S. 497, 511-513, 69 S.Ct. 201 (1948). This responsibility should include the duty to order an evidentiary hearing when appropriate, even if the moving party fails explicitly to request one.
. See, e. g., Ryan v. United States, supra note 4, 89 U.S.App.D.C. at 330, 191 F.2d at 781; Mattox v. United States, 146 U.S. 140, 148-149, 13 S.Ct. 50, 36 L.Ed. 917 (1892).
. Following the statement on diligence, the trial court concluded:
“I frankly say to * * * [defense counsel] that * * * the basis of your motion * * * namely, that there was a person from the Treasury Department * * * was not a basis for a new trial. Actually, there is no concealment of this, and the jury list does in fact recite [this fact] * *