OPINION OF THE COURT
VAN DUSEN, Circuit Judge.This appeal by Michael Newman challenges his June 22, 1972, sentence and judgment.1 Newman, who was at the *735time a City Councilman in McKeesport, Pennsylvania, had been convicted by a jury on Count I of a two-count indictment,2 which charged him with willfully procuring another person to intercept telephone conversations in violation of 18 U.S.C. §§ 2511(1) (a) and 2.3 We affirm.
The evidence adduced at Newman’s trial revealed that on March 3, 1970, Thomas Nee, a former Bell Telephone employee and a political associate of Newman, installed a tape recorder and activator on the telephone line of Mr. and Mrs. Eugene O’Neill. Nee, the chief Government witness, testified that Newman directed him to undertake the interceptions in order to collect politically useful information of the plans of Newman’s opponents (N.T. 93-94).
The interceptions continued for approximately one week. Each day Nee would service the recording device by removing the tape recorder from the telephone line and later playing the contents of the tape for Newman (N.T. 108-121). The tape recorder was discovered when Nee apparently inadvertently set it on broadcast, rather than record (N.T. 124). Nee was indicted for his participation and subsequently entered a plea of guilty.
The defendant urges each of three contentions as a basis for reversal:
I. The trial court erred when it denied him the opportunity to call the United States Attorney as a witness to impeach Nee’s credibility.
II. The trial court erred when it refused his request, made in the midst of the trial, to hear the contents of the tape found on the tape recorder. Neither the tape nor its contents were received in evidence.
III. The trial court committed plain error in its charge to the jury.
We shall consider these contentions in the above order.
I.
Newman contends that he has been denied his Sixth Amendment right to compulsory process. Specifically, he argues that the refusal by the trial court to allow him the opportunity to call the United States Attorney thwarted his efforts to impeach the credibility of Nee by showing a bargain had been reached between the Government and Nee concerning the sentence for Nee’s admitted participation in illegal electronic surveillance and his possible prosecution for perjury before the grand jury.
Newman claims Nee’s explicit denial of a bargain on cross-examination4 was *736inconsistent with the following statement made by the United States Attorney during a conference outside of the presence of the jury (“he” refers to Nee):
“He indicated if we indicate our good faith as best we can that he will disclose these facts at that time and we will then proceed to prosecute those persons who are responsible, but he has a Fifth Amendment right to I think avoid getting into those other offenses.” (N.T. 146)
Newman reads that statement to suggest that Nee had agreed to testify about previous wiretaps he had undertaken involving persons not connected with the trial in return for preferential treatment. However, the record, as a whole, makes clear that the United States Attorney’s statement does not support that contention. Nee, instead of agreeing to testify in future trials, “steadfastly refused to tell about them because he [was] in genuine fear of physical harm” (N.T. 145). The reason behind the out-of-court discussion, as the prosecutor made clear, was a concern that the court, by one of its questions, had opened the door to cross-examination concerning the details of the previous wiretaps. The United States Attorney felt that if Nee refused to answer the questions and relied on his Fifth Amendment right to remain silent, his credibility would be damaged.5
*737In the alternative, Newman suggests the United States Attorney’s statement may be read as a suggestion that Nee had agreed to disclose other facts in prosecutions against other persons in return for an indication of good faith by the prosecutor not to prosecute him for his possible previous perjury before the Grand Jury. This suggestion is equally misplaced. The court conducted a lengthy discussion out of the hearing of the jury, where the prosecutor denied the existence of any bargains, and he emphasized that his office had not reached a decision on whether to prosecute Nee for perjury.6
Although this court has consistently held that defense counsel has available the right to show that the testimony of a Government witness was given in reliance on a promise of a lighter sentence, or other preferential treatment, United States v. Murray, 445 F.2d 1171, 1174 (3d Cir. 1971); e. g., *738United States v. Migliorino, 238 F.2d 7 (3d Cir. 1956), the district court has wide discretion with respect to the examination of witnesses. Hayes v. United States, 329 F.2d 209, 218 (8th Cir. 1964). It may properly refuse to allow the defense to call the prosecutor if it does not believe that “he possesses information vital to the defense.” Gajewski v. United States, 321 F.2d 261, 268-269 (8th Cir. 1963); cf. Fisher v. United States, 231 F.2d 99 (9th Cir. 1956); see also United States v. Maloney, 241 F. Supp. 49 (W.D.Pa.1965).
The decision in Giglio v. United States, 405 U.S. 150, 92 S.Ct. 765, 31 L.Ed.2d 104 (1972), does not aid Newman’s claim that the district court’s refusal to allow him to call the United States Attorney mandates a new trial. The rationale underlying the Court’s determination in Giglio is inapplicable to the facts presented in this record. Giglio dealt with evidence of a promise of freedom from prosecution for a key government witness, discovered after the trial, which was inconsistent with explicit denials of leniency made both by that witness and the prosecutor during the trial. In that situation, the Court felt, the suppression by the prosecutor’s office of what was material evidence deprived the defendant of his due process rights as guaranteed in Napue v. Illinois, 360 U.S. 264, 79 S.Ct. 1173, 3 L. Ed.2d 1217 (1959), and Brady v. Maryland, 373 U.S. 83, 83 S.Ct. 1194, 10 L.Ed.2d 215 (1963). See Giglio, supra, 405 U.S. at 154-155, 92 S.Ct. 765.
Here, however, there is no evidence that the prosecutor suppressed evidence. The prosecutor explicitly denied to the court, on the record, both as a member of the bar and as an officer of the court, making any bargains or agreements with Nee. In United States v. Hykel, 461 F.2d 721 (3d Cir. 1972), the defendant contended that he had been prevented from showing that the testimony of a witness was prompted by her desire to avoid prosecution. Judge Hunter explained :
“The present case is not like Giglio v. United States, 405 U.S. 150, 92 S. Ct. 765, 31 L.Ed.2d 104 (1972). The opinion in that case makes clear that where a key Government witness has been promised that he will not be prosecuted if he testifies, a failure to disclose the promise may deny a defendant due process of law. In the present case, however, there is no evidence that the Government made any such promise to Mrs. Lawson.”
461 F.2d at 727; cf. United States ex rel. Dale v. Williams, 459 F.2d 763, 765 (3d Cir. 1972).
We believe that on these facts the court properly concluded that Newman’s request was “irrelevant to this case. ...” (N.T. 647).
II.
Newman next contends that the failure by the trial court to grant his request for the examination and use, if relevant, of a tape of the private phone conversations of the O’Neill family that had been made available to Nee prior to the trial, precluded him from developing his defense. This motion for discovery was made on the morning of the fourth day of the trial.7 Defense counsel did not seek to examine this tape even though Nee had concluded his testimony, including his cross-examination, and the prosecution had rested at the end of the third day of trial. The tape could have been requested and examined the pre*739vious evening without causing a trial delay.
An application for discovery under Rule 16 of the Federal Rules of Criminal Procedure is addressed to the sound discretion of the trial court, “and its ruling will be disturbed only for an abuse of discretion.” United States v. Fioravanti, 412 F.2d 407, 410 (3d Cir.), cert. denied, Panaccione v. United States, 396 U.S. 837, 90 S.Ct. 97, 24 L.Ed.2d 88 (1969); United States v. Randolph, 456 F.2d 132 (3d Cir. 1972). As Judge Aldisert has noted:
“Appellate courts have been increasingly reluctant to find that the denial of a particular discovery motion was an abuse of discretion in the absence of a showing that the defendant was prejudiced by such denial.” Fioravanti, supra, 412 F.2d at 410.
In addition, Rule 16(f) of the Federal Rules of Criminal Procedure provides that the trial .court may deny an untimely motion for discovery where the defendant has failed to show cause “why such motion would be in the interest of justice.” Cf. United States v. Conder, 423 F.2d 904 (6th Cir. 1970). The 1966 Advisory Committee Note to Rule 16 makes clear that one of the purposes behind Rule 16(f) is “to give the court sufficient control to prevent unnecessary delay and court time consequent upon a multiplication of discovery motions.” 8 Moore’s, Federal Practice, ¶ 16.01 [3], at 16-8 (2d ed. 1953).
After a careful examination of the record, we are unable to say that Newman was prejudiced by the court’s denial of his request. As stated above, Nee had completed his testimony, including his cross-examination, on the previous day. The tape was not introduced into evidence and the prosecutor never listened to it (N.T. 398).8 Moreover, the notes taken by Nee after he listened to the tape were provided to the defense for cross-examination.
Since the defendant has failed to demonstrate why the grant of his motion, which was made in the middle of the trial, would be in the interest of justice, the court properly denied it.
III.
The defendant’s final contention that the trial court’s facetious comments made during its charge constituted plain error is also without merit. See United States v. Newman, supra at note 1. Although the alleged “witty diversities” may have been unwise, we cannot say that they affected the substantial rights of Newman. F.R.Crim.P. 52(a).
For the foregoing reasons, the June 22, 1972, sentence and judgment will be affirmed.
. After the jury returned its verdict of guilty, Newman promptly filed a motion for new trial alleging 14 reasons in support. The trial court found the points urged by the defendant to be without merit, but 4% months later sua sponte *735granted a new trial based on its “injudicious indulgence in witty diversities.” The Government filed a petition for a writ of mandamus to compel the district court to vacate its order granting the new trial on the basis that the court’s order was entered not for reasons in the defendant’s timely new trial motion, but on grounds raised by the district court months after such motion and answer to such petition. The district court’s order was vacated and the defendant directed to appear for sentencing. United States v. Newman, 456 F.2d 668 (3d Cir. 1972).
. A motion for acquittal as to Count II of the indictment, which charged a violation of 18 U.S.C. §§ 2511(1) (c) and 2, was granted at the. completion of the Government’s case.
. 18 U.S.C. § 2511(1) (a) provides:
“(1) Except as otherwise specifically provided in this chapter any person who—
(a) willfully intercepts, endeavors to intercept, or procures any other person to intercept or endeavor to intercept, any wire or oral communication; . shall be fined not more than $10,000 or imprisoned not more than five years, or both.”
18 U.S.C. § 2 provides:
“(a) whoever commits an offense against the United States or aids, abets, counsels, commands, induces or procures its commission, is punishable as a principal.
“(b) whoever willfully causes an act to be done which if directly performed by him or another would be an offense against the United States, is punishable as a principal.”
. The following conversation took place between Nee and Newman’s counsel during cross-examination:
“Q. Sir, you have been made no promises or no threats have been made *736against you concerning your testimony in this case?
“A. No, sir, no threats have been made or no promises have been made.
“Q. Have you had any discussion with any member of the U.S. Attorney’s office concerning what information you will provide to the United States Attorney after sentence is imposed upon you?
“A. I have promised them nothing.
“Q. Have you made any indication to the United States Attorney’s office concerning what you might do in the event that they show their good faith?
“A. No, sir, I told them I would testify fully and truthfully in this case, and that is all I said I would testify under the other situations.
“Q. Was it then your indication to the United States Attorney's office that you would never testify against anybody except the defendant, Michael Newman.
“A. No, I didn’t say anybody. I said under certain situations that they were talking about. I didn’t say anybody.
“Q. Did you indicate a willingness after the United States Attorney’s office shows their good faith to cooperate further with them?
“A. No, sir. I said I would never testify in other incidents, that they would never get me on the stand.” (N. T. 318-19).
. In chambers the prosecutor stated:
“As I size him up, he is not pulling my leg, and it involves some racket connections in McKeesport, and I have tried to studiously avoid getting into that, and I am sure your Honor asked a perfectly logical question and maybe it would have been relevant in cross-examination anyway, but I am a little concerned about him being forced to answer these things because he seems to express a genuine fear of bodily harm with expression of distress of any disclosure of for whom these jobs were done.
“So far as we are concerned — and I hate like the dickens to have him take the Fifth Amendment out there in the courtroom, and I am in a quandary as to what to do. Now that your Honor has raised the question in doing other jobs—
“I don’t want to have [counsel] ask a question when he knows he is going to get a Fifth Amendment response because I think it goes improperly to the credibility of the witness. He has a constitutional right, but in this day and age, the Fifth Amendment, I think juries react to it . . . ” (N.T. 145, 146, 149).
We note, nevertheless, that except on grounds of relevancy, there was no limitation on defense counsel’s cross-examination of Nee. The trial judge said:
“ . . . conceivably [defense counsel] might ask some questions that were entirely outside of the ballpark and to which objection might be made and sustained without the necessity of the witness pondering whether he could safely answer them or not, but I suppose the proper procedure would be to wait until the questions are asked and then hear what objections are made . . . ” (N.T. 169-170)
. After Newman’s attorney repeated the statement made by the United States Attorney, the following conversation. took place at sidebar:
“ME. THOENBUEGH [United States Attorney] : What kind of a deal is that?
“THE OOUET: What does this have to do with this case? It is the gleam in the eye of Mr. Thornburgh to have some more.
“ME. LIVINGSTON [defense counsel] : I think it requires Mr. Thorn-burgh to answer the question whether or not he has made any promises not to prosecute Nee for perjury, whether he has made any promises. I think he must answer these questions, whether he has made any promises not to prosecute Nee for intimidating witnesses when the matter has been brought to his attention, and I think if he answers those questions in the negative, I think I fall flat on my face, and I am willing to rest. That is the thing in a nutshell, I think the record is clear, and, very frankly, in the present state of the record, although for the record I insist that he testify with the record clear, it doesn’t upset me a great deal if the court rules that he will not and I walk away and that is the end of the ballgame.
“THE COUET: It seems to me that it is unrelated to this case, that it is more about what he hopes to accomplish by a brilliant conviction in this case. Maybe he will get a couple more customers.
“ME. LIVINGSTON: Well, I am inclined, your Honor, to think that really there is no way — this witness was asked if he made any deals. He said no. I am talking about Nee. Now, I don’t know whether [the United States Attorney] hasn’t prosecuted him for perjury—
“ME. THOENBUEGH: . . . you know full well the practice of a prosecution office when a man purges himself of perjury. You know that. We don’t go around prosecuting people without giving them a chance. We can’t.
“ME. LIVINGSTON: Now, wait a second. I don’t mean this in the sense of unethical impropriety. I mean in the sense that I think it is improper for you to make the determination that he purged himself of perjury the second time.
“ME. THOENBUEGH: I make every determination in our office as to who is prosecuted, and you know full well we decline a basketful of prosecutions every week.
“ME. LIVINGSTON: But what you are doing here is saying, in effect, that he has purged himself of perjury the second time.
“ME. THOENBUEGH: I don’t know at this point, but I am not going to prosecute him at this point.
“ME. LIVINGSTON: For example, if it was brought to your attention that he perjured himself the second time—
“ME. THOENBUEGH: We could consider it. These are matters within the discretion of the prosecutor’s office, and I think this is just a grandstand play, your Honor, and I resent it very much. There is no basis in that scrap of paper for thinking a deal has been made with Mr. Nee.
“ME. LIVINGSTON: I think that becomes a jury question.
“ME. THOENBUEGH: You’re right, I said I hope we could make some more cases if this person gets rid of the idea everything is fixed in McKeesport, but the idea of—
“ME. LIVINGSTON: That he will disclose those facts at that time.
“ME. THOENBUEGH: . . .— we made no''deal. I didn’t say to Tom Nee, and there is absolutely no basis in that piece of paper for you making that kind of statement — ” (N.T. 644-646).
. The following conversation took place when Newman’s attorney requested the United States Attorney to provide him with any exculpatory evidence that had come to his attention:
“Mr. Livingston: I would request the opportunity to listen to this particular tape to determine what if any exculpatory matters may appear on it which can be used to the defendant’s benefit.
“The Court: Do you have any known exculpatory material?
“Mr. Thornburgh: I have none . I have never heard so much as one fragment of that tape.” (195a-196a, N.T. 397).
. Proof of the contents of the intercepted telephone conversations was not required to prove the charges against the defendant. Cf. United States v. Liddy, In Re Allen, 12 Crim.Law Reporter 2343 (D.C. Cir., Jan. 19, 1973).