opinion: Mr. Justice Stewart
  delivered the opinion of the Court.
  In 1956 two informations were filed in the United States District Court for the Northern District of Ohio charging the petitioner with having robbed banks in Waterville, Ohio, and Forest, Ohio. Represented by-counsel of his own choice, the petitioner waived indictment and pleaded guilty to both charges. Sentence was deferred pending a presentence investigation, and in the interim petitioner appeared as a defense witness at the jury trial of Marvin Breaton, charged with participation in the Waterville bank robbery. At that trial the petitioner testified that he had robbed the Waterville bank, but denied that Breaton had been with him. Breaton was convicted by the jury. Three weeks later the petitioner appeared with counsel before the District Judge for sentencing. During the course of the proceedings the judge inquired if counsel had any statement to make, but did not direct any similar inquiry to the petitioner personally. The court imposed sentence of twenty-five years imprisonment on the first information and fifteen years on the second, the sentences to run consecutively.
  In 1959 the petitioner instituted the present litigation by filing in the sentencing court a motion under 28 U. S. C. § 2255, to vacate and set aside the sentence he was serving. The motion alleged three grounds upon which it was claimed relief should be granted: that the petitioner’s pleas of guilty had not been voluntary, but had been induced by promises made by the Assistant United States Attorney in charge of the prosecution; that in violation of Rule 11 of the Federal Rules of Criminal Procedure the court had accepted the guilty pleas without first determining that they had been made voluntarily; and that in violation of Rule 32 (a) of the Federal Rules of Criminal Procedure the court had not inquired if the defendant wished to speak in his own behalf before sentence was imposed. The motion was denied by the District Court without a hearing, 184 F. Supp. 881. The Court of Appeals affirmed, per curiam, 280 F. 2d 379. We granted certiorari to consider seemingly significant questions as to the scope of relief under 28 U. S. C. § 2255. 365 U. S. 842.
  I.
  For the reasons stated in Hill v. United States, ante, p. 424, we hold that the failure of the District Court specifically to inquire at the time of sentencing whether the petitioner personally wished to make a statement in his own behalf is not of itself an error that can be raised by motion under 28 U. S. C. § 2255 or Rule 35 of the Federal Rules of Criminal Procedure.
  II.
  In support of his claim that his pleas of guilty had been involuntarily made, the petitioner’s motion and supporting affidavit set out detailed factual allegations. Specifically, the motion and affidavit alleged that on three separate occasions, identified as to time and place, an Assistant United States Attorney had promised the petitioner that he would receive a total prison sentence of not more than twenty years if he pleaded guilty to both infor-mations. These promises were said to have been made upon the authority of the United States Attorney and to be agreeable to the District Judge. It was alleged that the petitioner had been cautioned not to tell his own lawyer about the conversations. It was further alleged that when the petitioner threatened to advise his lawyer and the court of what had transpired, the Assistant United States Attorney had told him that if he “insisted in making a scene,” certain unsettled matters concerning two other robberies would be added to the petitioner’s difficulties. Finally, the motion and affidavit alleged that the petitioner had written two letters to the sentencing court and two letters to the Attorney General of the United States “relative to the misrepresentations” by the Assistant United States Attorney, to which he had received no reply.
  The Government filed a memorandum in opposition to the petitioner’s motion, attaching an affidavit of the Assistant United States Attorney. The affidavit emphatically denied any promises or coercion with respect to the petitioner’s pleas of guilty, but did admit that the Assistant United States Attorney had had a conversation with the petitioner in the county jail the day before Breaton’s trial, at which time the petitioner was told he was about to be given his last opportunity to tell the truth and that the court, in sentencing, might well take into consideration the petitioner’s refusal to talk.
  Without a hearing the District Judge determined that the petitioner’s allegations as to an agreement with the Assistant United States Attorney were false. The court noted that it had never received either of the two letters referred to by the petitioner, but had received a letter purportedly from him six months after sentencing, which did not mention any agreement, but simply requested that the sentences be made concurrent, rather than consecutive. The court further noted that the petitioner had not complained when no request for a reduction of sentence was made by the United States Attorney within sixty days after sentencing, and that instead, the petitioner had waited almost two and a half years to file the present motion.
  There can be no doubt that, if the allegations contained in the petitioner’s motion and affidavit are true, he is entitled to have his sentence vacated. A guilty plea, if induced by promises or threats which deprive it of the character of a voluntary act, is void. A conviction based upon such a plea is open to collateral attack. See Walker v. Johnston, 312 U. S. 275; Waley v. Johnston, 316 U. S. 101; Shelton v. United States, 356 U. S. 26, reversing, 246 F. 2d 571. “A plea of guilty differs in purpose and effect from a mere admission or an extra-judicial confession; it is itself a conviction. Like a verdict of a jury it is conclusive. More is not required; the court has nothing to do but give judgment and sentence. Out of just consideration for persons accused of crime, courts are careful that a plea of guilty shall not be accepted unless made voluntarily after proper advice and with full understanding of the consequences.” Kercheval v. United States, 274 U. S. 220, 223.
  The District Court recognized that the “charges of an agreement between a former Assistant United States Attorney and the defendant are serious,” and stated that if “this Court had any doubt as to their falsity it would require a hearing.” The court determined, however, that the combination of factual inferences already mentioned “conclusively indicates the falsity of the defendant’s allegations.” 184 F. Supp., at 883.
  We think the District Court did not proceed in conformity with the provisions of 28 U. S. C. § 2255, when it made findings on controverted issues of fact without notice to the petitioner and without a hearing. United States v. Hayman, 342 U. S. 205, 220. The statute requires a District Court to “grant a prompt hearing” when such a motion is filed, and to “determine the issues and make findings of fact and conclusions of law with respect thereto” unless “the motion and the files and records of the case conclusively show that the prisoner is entitled to-no relief.” This was not a case where the issues raised by the motion were conclusively determined either by the motion itself or by the “files and records” in the trial court. The factual allegations contained in the petitioner’s motion and affidavit, and put in issue by the affidavit filed with the Government’s response, related primarily to purported occurrences outside the courtroom and upon which the record could, therefore, cast no real light. Nor were the circumstances alleged of a kind that the District Judge could completely resolve by drawing upon his own personal knowledge or recollection.
  We cannot agree with the Government that a hearing in this case would be futile because of the apparent lack of any eyewitnesses to the occurrences alleged, other than the petitioner himself and the Assistant United States Attorney. The petitioner’s motion and affidavit contain charges which are detailed and specific. It is not unreasonable to suppose that many of the material allegations can either be corroborated or disproved by the visitors’ records of the county jail where the petitioner was confined, the mail records of the penitentiary to which he was sent, and other such sources. “Not by the pleadings and the affidavits, but by the whole of the testimony, must it be determined whether the petitioner has carried his burden of proof and shown his right to a discharge. The Government’s contention that his allegations are improbable and unbelievable cannot serve to deny him an opportunity to support them by evidence. On this record it is his right to be heard.” Walker v. Johnston, 312 U. S. 275, at 287.
  What has been said is not to imply that a movant must always be allowed to appear in a district court for a full hearing if the record does not conclusively and expressly belie his claim, no matter how vague, conclusory, or palpably incredible his allegations may be. The language of the statute does not strip the district courts of all discretion to exercise their common sense. Indeed, the statute itself recognizes that there are times when allegations of facts outside the record can be fully investigated without requiring the personal presence of the prisoner. Whether the petition in the present case can appropriately be disposed of without the presence of the petitioner at the hearing is a question to be resolved in the further proceedings in the District Court.
  There will always be marginal cases, and this case is not far from the line. But the specific and detailed factual assertions of the petitioner, while improbable, cannot at this juncture be said to be incredible. If the allegations are true, the petitioner is clearly entitled to relief. Accordingly, we think the function of 28 U. S. C. § 2255 can be served in this case only by affording the hearing which its provisions require.
  Vacated and remanded.
  The Chief Justice, Mr. Justice Black, Mr. Justice Douglas and Mr. Justice Brennan concur in the Court’s judgment and opinion except as to Part I, from which they dissent for the reasons set out in their dissent in Hill v. United States, ante, p. 430.
  The affidavit filed with the petitioner’s motion was as follows:
  “John Machibroda, having been duly sworn according to law deposes and says that he is the petitioner in an action filed in this Court entitled 'Motion To Vacate sentence’ and this affidavit is made in support thereof:
  “1. That affiant was interviewed in the County Jail on or about February 21, 1956, by one Clarence M. Condon who represented himself to be as Assistant United States Attorney in charge of the prosecution of alleged bank robberies committed at the Waterville and Forest Banks. (Later designated as Cases 10345 and 10348). The County Jail where the interview took place is situated in Toledo, Ohio.
  “2. That the said Clarence M. Condon represented to the Affiant that he had the authority to speak for the United States Attorney and the United States District Judge in the matter of the amount of sentence that would be imposed in Cases Nos. 10345 and 10348.
  “3. That the said Clarence M. Condon represented to the Affiant that if the Affiant would waive indictment in case no. 10348 and plead guilty in cases Nos. 10345 and 10348 the Court would not impose a sentence in the excess of twenty (20) years in Case No. 10345 and that any sentence imposed in Case No. 10348 would not be in the excess of ten (10) years and would be ordered served concurrently with the term imposed in case No. 10345.
  “4. That on the assurance of the said Clarence M. Condon that the sentences would be imposed as heretofore set out in paragraph 3, above, the Affiant agreed to waive indictment in case no. 10348 and plead guilty to both cases* (This interview was held on or about February 21, 1956.)
  “ *At that time the Affiant had already waived indictment in case No. 10345.
  “5. That the said Clarence M. Condon instructed the Affiant to advise his Attorney, John Schuchmann, that he would waive indictment in case no. 10348 and plead guilty to both eases.
  “6. That the said Clarence M. Condon cautioned the Affiant to refrain from advising the said John Schuchmann of his interviews with Mr. Condon and that an agreement had been reached between the government as represented by Mr. Condon, and the Affiant in the matter of waiver, pleas and sentences.
  “7. That on February 24, 1956, Affiant acting on the promises and representations of the said Clarence M. Condon waived indictment in case no. 10348.
  “8. That on February 24, 1956, the Affiant acting on the promises and representations of the said Clarence M. Condon pleaded guilty in Cases Nos. 10345 and 10348.
  “9. That on or about May 22, 1956, the said Clarence M. Condon again interviewed the Affiant at the County Jail and informed Affiant that because of Affiant’s unfavorable testimony at the trial of a co-defendant the Court was vexed and there might be some difficulty in regards to the promised twenty (20) year sentence.
  “10. That the said Clarence M. Condon admonished the Affiant that he had tried to warn him during the trial of the co-defendant that Affiant would shortly appear before this Court for sentence*
  “ *The exact words Mr. Condon used to warn the Affiant are to be found in the transcript of the trial of Marvin Ferris Breaton.
  “11. That at no time did the Affiant ever represent to Mr. Condon or anyone else that he would testify one way or the other at the trial of the co-defendant. The promise of the maximum sentence of twenty (20) years was predicated solely on the Affiant’s agreement to waive indictment and plead guilty to both informations.
  “12. That the Affiant immediately became agitated and hotly informed Mr. Condon that he was going to tell his Attorney the whole story and demand that the Court be informed of the agreement.
  "13. That the said Clarence M. Condon assured the Affiant that in the event a sentence in the excess of twenty (20) years was imposed the United States Attorney, himself, would move within sixty (60) days for a reduction of the portion of the sentence in excess of twenty (20) years; that the Affiant had nothing to worry about if he kept his mouth shut; that on the other hand, if Affiant insisted in making a scene in a matter of his own making, there were the unsettled matters of the robberies of the Trotwood and Canal Fulton Banks which would be added to the Affiant’s present difficulties.
  “14. That on May 23, 1956, the Affiant was sentenced by the Honorable Frank L. Kloeb to twenty-five (25) years in Case No. 10345 and fifteen (15) years in case no. 10348.
  “15. That immediately after sentence in an interview with the said Clarence M. Condon, the Affiant was informed he had no reason to worry for as soon as the Judge ‘cooled off’ the United States Attorney would have the sentence reduced to twenty (20) years as had been promised.
  “16. That within a few hours after sentence, the Affiant was on his way to the Federal Penitentiary, Leavenworth, Kansas.
  “17. That the sentence was not reduced in sixty (60) days and has not been reduced to date.
  “18. That the petitioner wrote two (2) letters to the Honorable Frank L. Kloeb and two (2) letters to the Attorney General of the United States relative to the misrepresentations by the said Clarence M. Condon. These letters were posted in the official prisoner’s mail box and the Affiant has failed to receive a reply to any of them.
  “19. That the Affiant’s previous experience with Court officials has been with the authorities representing the Canadian Government and he found them to honor their commitments. He had no reason to believe that the officials of the United States Courts would do otherwise. His naivete has cost him an extra twenty (20) years in prison.”
  See also Daniel v. United States, 107 U. S. App. D. C. 110, 274 F. 2d 768; Teller v. United States, 263 F. 2d 871; Watson v. United States, 104 U. S. App. D. C. 321, 262 F. 2d 33; Euziere v. United States, 249 F. 2d 293; Motley v. United States, 230 F. 2d 110; United States v. Paglia, 190 F. 2d 445.
  Section 2255 of Title 28, United States Code, provides in part: “Unless the motion and the files and records of the case conclusively show that the prisoner is entitled to no relief, the court shall cause notice thereof to be served upon the United States attorney, grant a prompt hearing thereon, determine the issues and make findings of fact and conclusions of law with respect thereto. If the court finds that the judgment was rendered without jurisdiction, or that the sentence imposed was not authorized by law or otherwise open to collateral attack, or that there has been such a denial or infringement of the constitutional rights of the prisoner as to render the judgment vulnerable to collateral attack, the court shall vacate and set the judgment aside and shall discharge the prisoner or resentence him or grant a new trial or correct the sentence as may appear appropriate.”
  Section 2255 of Title 28, United States Code, also provides, in part: “A court may entertain and determine such motion without requiring the production of the prisoner at the hearing.”