In late morning on February 6, 1973, four men robbed a Crocker National Bank in Los Angeles. Three men were brought to trial in April, 1973, for the offense: defendants Tommie Louis

Brown, Robert Lee Nobles, and Virgil David Swain. The fourth man, whose name appeared on the indictment as Jonathan Ray Nobles, was a fugitive at time of trial.

The government’s theory was that Brown jumped behind the tellers’ windows and moved down the line of cages, collecting money from the cash drawers, while the other three guarded the customers and personnel from various positions. A surveillance camera took pictures of all the participants except the one who stood beneath the camera, allegedly defendant Nobles [hereinafter Nobles].

I. The Brown and Swain Appeals

The evidence against Brown and Swain was similar and consisted of surveillance photographs, items taken from the apartment they shared, a comparison of photographs, eyewitness identifications, and a statement by Brown.

Defendants Brown and Swain primarily attack the comparison of certain photographs. One group of photographs, consisting of enlarged surveillance pictures showing the faces and clothing of the two robbers alleged to be Brown and Swain, were placed on a chart next to a second group of photographs consisting of enlarged police pictures of Brown and Swain as well as FBI photographs of the items of clothing seized from their apartment. An FBI expert in photographic identification, Frederick E. Webb, compared the two groups of photographs and stated that the faces in the police photographs were the same faces as those in the surveillance photographs. He also testified that the clothing in the two groups of photographs was the same, and further, he made a similar analysis of a surveillance photograph of a pistol used in the robbery and a FBI photograph of the handgun seized in the apartment.

When Mr. Webb, in response to the prosecutor’s questions, began to state his opinion that Brown and Swain were indeed two of the three pictured on the surveillance film, the district court overruled the defense objection but not without some misgiving:

Reporter’s Transcript [hereinafter R.T.] 260, lines 5-11. We too are troubled by the proffered testimony.

In Cairns , this circuit previously wrote:

434 F.2d at 644 .

Advisory Committee’s Note to Proposed Federal Rule of Evidence 702, 56 F.R.D. 183 , 282 (1972). To permit an expert to testify as to his opinion of parentage based on the resemblance of a child to a reputed father in a paternity suit would be grossly inappropriate by the above standard. But just as surely, fingerprint identification, the comprehensive examination of aerial photographs, and other similar scientific and technical evaluations, are obviously within the realm of permissible expert testimony. Testimony as to whether a particular individual is portrayed in a photograph rests on some middle ground. Since the Cairns decision relied solely upon traditional expertise fields, we feel it incumbent upon ourselves to reexamine the issue faced in Cairns .

We have requested and reviewed the briefs submitted in Cairns . Such review allows us to conclude that the two cases — Cairns and the instant one — are distinguishable.

In the instant case, Webb’s testimony was general. In reference to the photographs of Brown, he stated broad conclusions : “rather thin-faced,” “somewhat elongated,”. “[t]he mustache is similar, the shape of the nose, the eyes, the eyebrows, . . . .” R.T. 260, lines 22-24. In Cairns , however, the testimony was of greater detail. Not only did the agent compare general contours and shapes but also found ear and lobe formations particularly significant and termed a particular facial crease as “distinctive” and “unusual.” Government’s Brief, United States v. Cairns, p. 5. In its argument to this court in Cairns , the government also emphasized the detail of the agent’s testimony, for example, his comparison of a nipple in the center of the defendant’s ear. Id. at 6.

We would hold that Cairns should be limited to the precision as argued in its briefs; therefore, when a party seeks to introduce expert testimony on personal photographic identification — whether to prove or disprove similarity, he should first be required to make an offer of proof to the court outside the presence of the jury.

After the elicitation of what facts the expert has depended upon in reaching his conclusions, the court should determine whether it has been convinced by a preponderance that the facts offered are beyond the jury’s common experience. Of course, the court in reaching its determination must take into consideration that the party desiring admission may be free to argue his position without the benefit of expert testimony. If the court in its discretion, which may not be disturbed absent clear abuse, is convinced that the expert may materially assist the jury beyond their common experience as amplified by argument of counsel, the expert should be allowed to testify.

The same general test should be applied to the photographic identification and comparison of inanimate objects. The trial courts, however, should be cognizant that while the everyday ex *150 periences of twelve laymen over their combined lifetimes may permit them to make photographic comparisons of persons, they may utterly lack experience to distinguish or recognize certain objects such as firearms. In the facts of this particular case, we would hold the admission of the expert’s opinion on the personal identification of Brown and Swain to have been error, 1 but his testimony concerning the items seized to have been properly admitted. We cannot conclude, however, that the error. was prejudicial. Disregarding the agent’s opinion as to their identity, the evidence against Brown and Swain — the eyewitness testimony, the discovery of the items — was overwhelming, rendering the error harmless.

II Nobles Appeal

The evidence against Nobles differs from the case against Brown and Swain. Most obvious is the' absence of surveillance photographs, for Nobles is alleged to have been the robber who stood underneath the camera rather than within its scope. Second, no objects were found to connect him to the offense in contrast to the items seized at the apartment of Brown and Swain. Finally, the eyewitness testimony was far less impressive against Nobles than against Brown and Swain.

A bookkeeper at the bank identified Brown and Swain in court as well as the items of clothing. He could not identify Nobles. Similarly, the assistant branch manager identified Brown and Swain in court but could not identify Nobles.

A bank teller, Peter Van Gemeren, identified Brown in court. He did identify Nobles but his testimony was subjected to extensive cross-examination. Likewise, Gary Hoffman, a salesman visiting the bank, pointed out the men alleged to be Brown and Swain on the surveillance photographs and described their activities; he too identified Nobles as having stood by the business counter. Defense also subjected Hoffman to arduous cross-examination.

Although Nobles presented an affirmative alibi defense, his strongest attack was to discredit the key evidence against him: the eyewitness identification by Van Gemeren and Hoffman. To do so, his counsel not only employed cross-examination but also attempted to introduce expert opinion testimony on the frailties of eyewitness examination in general and to impeach the specific eyewitnesses by statements made by them to his investigator.

A. Expertise on Eyewitness Identification

Nobles offered the testimony of Dr. Robert Buckhout as an expert witness to describe the problems of eyewitness identification in general and the specific difficulties with the identifications in this case. The court refused the proffered testimony, concluding that the testimony would invade the province of the jury, that the undue consumption of time would substantially outweigh its probative value, and that the offer of proof was inadequate. We in turn cannot conclude that the trial court was in *151 error. United States v. Amaral, 488 F.2d 1148 (9th Cir. 1973).

B. Impeachment

During the defense case, counsel sought to introduce the testimony of John Bond, chief investigator for the Federal Public Defenders. Mr. Bond had interviewed the witnesses Van Gemeren and Hoffman. On cross-examination Van Gemeren had testified that he did not recall telling Bond that he had seen only the back of the bank robber beneath the camera; Hoffman, during cross-examination, had denied telling Bond that all blacks look alike. Defense counsel’s offer of proof was that Mr. Bond would testify that Hoffman had told him that “all blacks look alike” and that Van Gemeren had told him that “as far as the man at the surveillance camera is concerned, he [Van Gemeren] only saw the back of that man.” Eventually, the court ordered that impeachment of the witnesses by Bond through these statements would be conditioned upon the defense agreeing to render to the government upon completion of the investigator’s testimony the alleged statements as contained in the investigator’s report. Bather than submit to this condition, defense counsel chose to forego impeachment, preferring to stand upon his client’s right against self-incrimination as well as the protection of a work product rule.

For the reasons stated below, we would hold that, despite the very limited and seemingly judicious restriction on the defense, conditioning impeachment with prosecutorial discovery was prejudicial error. Admittedly, the order was narrowly drawn. But to single out any one witness and require as a condition precedent that his ' previous statement be produced is inappropriate. The defendant must have the essential right to call an impeaching witness; he need not corroborate the credibility of that witness before calling him to the stand, i. e., by producing a prior recorded or transcribed statement. Were it otherwise, we would fear that such requested discovery would become a matter of routine, a result we desire to avoid.

Although defense counsel did not argue that the condition impinged on the attorney-client privilege, we deem it appropriate to comment on the relevance of that privilege.

The proposed Rules of Evidence as tentatively promulgated by the Supreme Court [hereinafter Court version] included Rule 503, Lawyer-Client Privilege. 56 F.R.D. 183 , 235-240 (1972). That rule in pertinent part states:

Id. at 236 . In contrast, the tentative draft of H.R. 5463, 93rd Cong., 1st sess., as amended by the Subcommittee on Criminal Justice, House Committee on the Judiciary [hereinafter House version] , contains no specific privilege rules. The House version would promulgate only a general rule, Rule 501, which pro^-vides that privileges “shall be governed by the principles of the common law as they may be interpreted by the courts of the United States in the light of reason and experience . . . .” U.S.L.W., Supplement, p. 6, July 17, 1973. The rule does, however, further provide that the Supreme Court may prescribe rules pursuant to statutory authority. Thus, the Supreme Court may some day prescribe rules such as Rule 503 of its version, the literal meaning of which may arguably serve to protect a communica *152 tion as existed between the investigator and counsel for the defense.

But absent any prescribed rules, common law dictates the federal rules of evidence, and the common law does not protect communications from third persons:

8 Wigmore, Evidence (McNaughton rev. 1961), § 2317(2) (emphasis original).

Defense counsel did strongly assert that to condition impeachment in the manner ordered could infringe upon his client’s right against self-incrimination. This problem is indeed troubling.

When Federal Rule of Criminal Procedure 16 was amended in 1966, Justices Black and Douglas dissented. Justice Black wrote: “I am reasonably certain, however, that the Court’s transmittal does not carry with it a decision that the amended rules are all constitutional. . And I agree with my Brother Douglas that some of the proposed criminal rules go to the very border line if they do not actually transgress the constitutional right of a defendant not to be compelled to be a witness against himself.” 39 F.R.D. 252 , 272 (1966). And Justice Douglas stated:

39 F.R.D. at 277 (footnote omitted).

The “distinguished state court” decision, referenced in the omitted footnote, is Jones v. Superior Court, 58 Cal.2d 56 , 22 Cal.Rptr. 879 , 372 P.2d 919 (1962). In Jones , the defendant charged with rape requested a continuance of trial, alleging that he had been impotent for a long time, and the continuance was necessary to gather essential medical evidence. The prosecution responded with a motion for discovery of witnesses, reports, and data concerning the alleged impotence. In holding that the prosecu-torial discovery was proper, the California Supreme Court concluded that “since the criminal discovery permitted to the defendant is the result not of a consti *153 tutional mandate of due process but rather of the desire to promote orderly ascertainment of truth [discovery] should not be a ‘one-way’ street.” G. Lapides, Cross-Currents in Prosecutorial Discovery: A Defense Counsel’s Viewpoint, 7 U.S.F.L.Rev. 217, 219 (1973), citing Jones v. Superior Court, 58 Cal.2d at 59-60 , 22 Cal.Rptr. 879 , 372 P.2d 919 .

More recently, however, the California Supreme Court has virtually limited Jones to its facts. In Prudhomme v. Superior Court, 2 Cal.3d 320 , 85 Cal.Rptr. 129 , 466 P.2d 673 (1970), the court wrote:

Id. at 323, 325, 326, 85 Cal.Rptr. at 131 , 466 P.2d at 675 (footnotes and citations omitted; emphasis supplied).

The California Supreme Court is not alone in this respect. In United States v. Fratello, 44 F.R.D. 444, 449, 451 (S.D.N.Y.1968), Judge Pollack concluded:

Citations omitted; emphasis supplied.

Yet, Prudhomme and Fratello dealt with pretrial prosecutorial discovery as well as the constitutional concerns of conditioning defense discovery upon the possibility of enhancing the government’s case in chief. In the instant case, of course, the discovery would have been during trial and useful only in rebuttal. Then, too, both Prudhomme and Fratello preceded Williams v. Florida, 399 U.S. 78 , 90 S.Ct. 1893 , 26 L.Ed.2d 446 (1970), which upheld the constitutionality of a state’s notice of alibi statute in the face of fifth amendment assault. We would, nevertheless, conclude that the fifth amendment remains relevant in the instant circumstances.

In United States v. Wright, 489 F.2d 1181 (D.C.Cir. 1973), the Circuit for the District of Columbia faced an analogous situation. The appellant’s court-appointed counsel had employed an investigator from the Public Defender Service. The investigator interviewed potential witnesses and sent to counsel a report consisting of summaries of the interviews. At trial the court ordered the investigator who had testified in behalf of the defense to turn over a copy of the report to the government. True, the order was to forward the entire report rather than to specific, relevant portions as were ordered here, but potential incrimination exists in both circumstances.

The court concluded that the principle that criminal discovery must inevitably remain basically a one-way street is firmly imbedded in our common law tradition. Id. at 1192 . As that circuit also noted,

Id. at 1194. (Emphasis added). In the instant case, the defense prior to the cross-examination of the government’s witnesses surely could not have intended to reveal its own information when the witnesses may have admitted its import during cross-examination. And if the witnesses had admitted that they had made such statements as “all blacks look alike” or “I only saw him from the back” to the investigator, the government would have had the responsibility of resurrecting its witnesses’ testimony by *155 eliciting any rehabilitating statements by those same witnesses. 2

Since the witnesses, for whatever reasons, denied making the initial damaging statement, the defense had no alternative but to present its impeachment evidence, i. e., Bond’s testimony. 3 If the prosecutor doubted the validity of the contexts in which the purported statements were made as testified to by Bond, he surely had access to his own witnesses and by their testimony could have offered rebuttal to Bond’s version. In summary, then, we agree with the Circuit for the District of Columbia that

Id. at 1195. See also People v. Bais, 31 Cal.App.3d 663 , 107 Cal.Rptr. 519 (1st Dist. 1973).

The Wright panel also examined that discovery order from the perspective of the Federal Rule of Criminal Procedure 16 and the Jeneks Act, 18 U.S.C. § 3500 , 4 as we must.

Before the promulgation of the original rules of criminal procedure, it was doubtful whether criminal discovery was permitted. In 1966, however, Rule 16 was liberalized toward greater discovery.

The pertinent portions of Rule 16 are as follows:

Emphasis and capitalization added.

Each subsection contains a work product 5 savings clause, i. e., the italicized portions. But the government’s work product is subject to an important exception, the Jencks Act, 18 U. S.C. § 3500, which provides in relevant part:

Thus, while Rule 16 is framed in terms of pretrial discovery, its inclusion of the Jencks Act leads us to conclude that Rule 16 has relevance to discovery during trial. And specifically, defense may discover, for purposes of impeachment, statements of government witnesses who have testified. But no such exception is included within the terms of subsection (c). We would conclude that the work product of defense is inviolable in these circumstances. 6 See also, United States v. Wright, 489 F.2d 1181, 1189-1190 (D.C.Cir. 1973).

Finally, the court may make brief comment upon the alleged misconduct of the prosecutor. A review of the entire transcript permits us to conclude that the prosecutor’s conduct does not require reversal. In fact, the record indicates that the trial judge conducted the case most properly, and the defendants received a fair trial.

Affirmed in part, reversed in part, remanded.

. The photographs introduced in this case afford a spectrum for aiding a trial court in determining when expert testimony may be permitted. There can be no reasonable doubt that the pictures of the robber who moved from cage to cage was indeed defendant Brown. The resolution of the camera is clear; his likeness unmistakable. Testimony of an expert would be of no useful purpose and hence error, but presumably, harmless.

The pictures of the man who stood to the rear of the bank are of poor resolution and quality. The only articulable characteristics concerning which the expert could testify were generalities, e. g., facial contours, shape of sideburns. This foundation would be inadequate, and expert testimony would be error, perhaps prejudicial, depending upon the state of other evidence.

The third pictured individual was the fugitive, allegedly Jonathan Nobles, brother of defendant Nobles. The resolution of the surveillance pictures is clear, but the conclusion that the individual is Jonathan Nobles after comparison with a known photograph of Jonathan Nobles is not entirely free of doubt. An expert, in our opinion, could be useful. Of course, the discretion would lie with the trial court.

. Enterprising counsel may arguably assert that the evidence doctrine of completeness, e. g., Cal.Evid.Code § 356 and Proposed Federal Rules of Evidence, Court version 107, House version 106, would require disclosure. But as the comment to § 356 by the Assembly Committee on the Judiciary implies, the doctrine is not a discovery device, but rather, only permits certain relevant evidence to be admitted that would otherwise be inadmissible. The burden is on the adversary to “inquire,” that is, cross-examine or rebut.

Since the Proposed Federal Rule may shift that burden, i. e., the adversary may “require” admission of the entirety, it would conceivably be utilized as a discovery tool. But tire proposed rule only encompasses writings or recorded statements introduced into evidence, not the testimony of an individual, albeit that his recollection may be memorialized.

. That impeachment is the only alternative was not lost to the prosecutor. At the close of trial, he argued:

Mr. MacIntyre: . . . Mr. Bond never testified in the trial as to anything Mr. Hoffman did or did not say to him.

Mr. Hoffman, you heard his testimony, and I submit to you he denied the questions, said, “No,” to the questions that were asked by Mr. Allis. If he testified any differently Mr. Bond would have testified in this courtroom to you as to what the inconsistencies were, and Mr. Bond did not so testify. You heard his testimony.

R.T. at 745, lines 6-14.

. The panel in Wright gave due consideration to the problem which could arise if a witness refreshed his recollection. (There is nothing in the record to suggest Bond used his reports to refresh his recollection.) That court considered it “hornbook rule of evidence that, had [the investigator] used parts of his report to refresh his recollection while on the witness stand, the prosecution would be entitled to examine those parts of the report and would be permitted to make use of those parts of the report in cross-examining [him].” 489 F.2d at 1188 (emphasis added). As noted by that panel, however, refreshing recollection prior to testifying may stand in different posture. See McGill v. United States, 270 F.2d 329 , 331, 106 U.S.App.D.C. 136 (1959) ; see also, Sullivan v. Superior Court, 29 Cal.App.3d 64 , 105 Cal.Rptr. 241 (1st Dist. 1972) [attorney-client privilege applicable when client previously refreshes recollection].

The Court version of Proposed Rule 612 generally permits an adversary to inspect, cross-examine from, and introduce portions of a writing used by a witness to refresh his recollection either before or while testifying. The House version has amended this by requiring the court in its discretion to determine that it be necessary in the interest of justice before a writing be divulged that has been used for prior refreshing of recollection.

. To apply the work product rule to criminal law is not unusual:

In re Grand Jury Proceedings, Duffy v. United States, 473 F.2d 840, 846 (8th Cir. 1973).

. We may note that new proposed amendments to the Federal Rules of Criminal Procedure are pending and have been stayed by Congress until August 1, 1975. It must be noted that the proposed changes include the addition of Rule 12.1, Notice of Alibi, and 12.2, Notice of Defense Based Upon Mental Condition. Also, Rule 16 has undergone revision ; of particular note is the revised Rule 36(b), Disclosure of Evidence by the Defendant :

It must be emphasized, however, that Rule 16(b)(2), Information not subject to disclosure, retains the inviolability of internal defense documents.