OPINION OF THE COURT
ROTH, Circuit Judge.I.
Appellant Calvin Thomas was convicted of conspiracy to steal government property, interstate transportation of stolen goods and theft of government property. This appeal concerns the prejudicial effect of the introduction at trial of the guilty pleas of Thomas’s co-conspirators. Defense counsel moved in limine for the exclusion of the guilty pleas based on a pledge that he would not elicit any information about the pleas from the co-conspirators. The district court denied the motion, holding that the guilty pleas were being introduced for a proper purpose and that the court’s limiting instructions to the jury would cure any prejudice to the defendant. We hold that the admission of this evidence by the district court constituted er*1204ror so prejudicial that it requires reversal of Thomas’s conviction.
II, .
Appellant Calvin Thomas worked for the United States Army as a civilian heavy mobile equipment inspector and was a member of the Army Reserve, where he served as a property book officer. Thomas participated in an Army Reserve road-building project in Honduras in 1988. Thomas was responsible for overseeing the repair and return of road-building equipment that was borrowed from the 99th Army Reserve Command in Oak-dale, Pennsylvania. The equipment was shipped from Honduras to Fort Meade, Maryland, where it was serviced and repaired before being returned to the 99th Command.
As the repair and return project neared completion, Thomas realized that many extra parts would remain. Thomas made arrangements with two fellow reservists, Wendell Charles and Charles Copney, to ship roughly $30,000 worth of spare parts in three tractor-trailer loads to Charles’s and Thomas’s private garages in Hopwood, Pennsylvania,-Copney, an Army Reservist and truck driver, transported the spare parts to Hopwood Enterprises, Charles’s firm. Both Charles and Copney pled guilty to conspiracy and to theft of government property and both testified against Thomas as part of their plea agreements.
Thomas did not dispute that in violation of Army regulations he arranged with Charles and Copney to transport Army material and to store it at his own garage and at Charles’s company’s facilities.. However, Thomas maintained that he had no intention, of stealing the transported property. Thomas argued that he at all times intended to transfer the parts and equipment back to the Army base where be worked as the need for the parts arose. Thomas argued that Army regulations would have prevented his unit from retaining the spare parts had he properly logged them and returned them to the 99th Command.
Thomas did in fact return a substantial portion of the Army equipment before his arrest. However, Charles testified that news of an impending police search motivated Thomas to call him and tell him to conceal any government parts remaining at Hopwood Enterprises. Copney also testified that he intended to steal the spare parts. Thus, the issue of Thomas’s specific intent was the major focus of testimony at trial, making the introduction of evidence of the co-conspirators’s guilty pleas particularly damaging to Thomas’s defense.
Prior to the introduction at trial of evidence of the guilty pleas of Thomas’s co-conspirators, defense counsel made a motion in limine for the exclusion of such evidence. Defense counsel disavowed any intention to use the co-conspirators’s guilty pleas to impeach, their credibility. The district court denied.the motion. Both Charles and Cop-ney testified against Thomas and their guilty pleas were elicited on direct examination by the government. The district court' gave cautionary instructions to the jury concerning the testimony of Charles and Copney both before and after their testimony.
In ruling on a post-trial motion by Thomas for his release pending appeal, the district court revisited the propriety of admitting the guilty pleas and succinctly restated its reasons for admitting the evidence:
[T]he government properly introduced evidence of the guilty pleas to aid the jury in assessing Copney’s and Charles’ credibility, to establish Copney’s and Charles’ ac-knowledgement of their participation in the offense, and to counter the inference that Copney and Charles had not been prosecuted, and that Thomas alone had been prosecuted....
D.Ct. opinion of January 14, 1992, at 11.
The jury found Thomas guilty of conspiracy to steal government property, interstate transportation of stolen goods and theft of government property. - Thomas was sentenced to twenty-four months imprisonment.
IV.
The jurisdiction of the district court rested upon 18 U.S.C. § 3231. The appellate jurisdiction of this Court is pursuant to 28 U.S.C. § 1291.
*1205The district court relied on several eases in which evidence of co-conspirators’s guilty pleas was admitted for limited purposes. This Court has repeatedly recognized that evidence of a co-conspirator’s guilty plea may be introduced at trial for two purposes: first, to blunt the impact on a government witness’s credibility of having evidence of a guilty plea and plea agreement brought out on eross examination by the defense, and, second, to prevent any improper inference by the jury that the defendant has been singled out for prosecution while the co-conspirators have not been prosecuted. See United States v. Gambino, 926 F.2d 1355, 1363 (3d Cir.1991) (guilty plea introduced to blunt attack on credibility); United States v. Inadi, 790 F.2d 383, 384 n. 2 (3d Cir.1986) (guilty plea introduced to prevent inference of selective prosecution).
However, the reasons of the district court for admitting the evidence of Charles’s and Copney’s guilty pleas are inadequate to support the risk of jury prejudice, under the facts of this case. In general, we have allowed evidence of guilty pleas to bolster the credibility of government witnesses. The district court here stated in denying the defense motion that evidence of the guilty pleas “goes to the [witnesses’] credibility.” See transcript of June 24, 1991, at 8. In Gambino, this Court upheld the introduction of co-conspirators’s guilty pleas, stating:
In any criminal trial, the credibility of the prosecution’s witnesses is central. By eliciting the witness’ guilty plea on direct examination, the government dampens attacks on credibility, and forecloses any suggestion that it was concealing evidence.
Gambino, 926 F.2d at 1363 (citations omitted). However, as represented by defense counsel, no challenge to the witnesses’ credibility based on their plea agreements with the government was forthcoming on cross-examination. Thus, there was no need to protect the credibility of the prosecution’s witnesses from attack by allowing the preemptive introduction of evidence of their guilty pleas.
The second justification offered by the district court, that the jury would impermissibly conclude Thomas alone was being prosecuted, does not justify admission of his co-conspirators’s guilty pleas. In the sole case in this Circuit directly citing this reason to support admitting a co-conspirator’s guilty plea, United States v. Inadi 790 F.2d 383 (3d Cir.1986), the district court admitted evidence of the guilty pleas only “in order to rebut defense counsel’s persistent attempts on cross-examination to raise an inference that the co-conspirators had not been prosecuted, and that defendant was being singled out for prosecution.” Id. at 384 n. 2. In this case, the district court certainly could have instructed the jury that they need concern themselves only with the guilt or innocence of defendant Thomas and that the involvement of any other persons in any alleged scheme was not this jury’s concern. There was no need to mention'the guilty pleas to deter any concern that Thomas was being-singled out for prosecution.1
The third reason offered in support of the admission of the guilty pleas by the district court was that such evidence would “establish Copney’s and Charles’ acknowledgement of their participation in the offense.” D.Ct. opinion of January 14, 1992, at 11. Yet, Copney and Charles testified about their roles in the transportation of the stolen property involved without facing any challenge from the defense. The defense in this case even acknowledged the defendant’s participation in all of the actions constituting the offense. The only issue at trial was whether Thomas had the requisite intent to conspire to steal government property. Thus, the defense did not raise any of the three possible challenges to the credibility of the government witnesses that might have justified the district court’s admission of the evidence of the guilty pleas — the defense pledged not to raise the guilty pleas on cross-examination, the . defense did not raise inferences that Thomas alone was being prosecuted, and the defense did not challenge the participation of *1206the co-conspirators or even the defendant in the actions that constituted the crime.
While the credibility of the prosecution’s witnesses may be “central” in a criminal case, as noted by this Court in Gambino, the requirement that a defendant receive a fair trial is nevertheless supreme, and the introduction of a co-conspirator’s guilty plea without a proper purpose may deprive a defendant of a fair trial:
Even if otherwise appropriate, the challenged references to guilty pleas could still constitute reversible error if used as substantive evidence of the defendants’ guilt. As we have noted, such use poses the threat that a defendant will be found guilty not on the basis of the evidence against him but on the basis of a shadow cast by cases against others.
Gambino, 926 F.2d at 1367 (citations omitted). As the only issue at trial was Thomas’s intent, and none of the three reasons offered by the district court for admitting evidence of the guilty pleas withstands scrutiny, the likely effect of Charles’s and Copney’s guilty pleas was to suggest improperly to thé jury that Thomas was also guilty of conspiracy.
In several cases where evidence of a co-conspirator’s guilty plea was entered, we have held that proper limiting instructions from the court cured the possible prejudice to the defendant. In its preliminary instructions to the jury, the district court stated: “[T]he fact that ... Copney and ;.. Charles have pleaded guilty to a crime is not evidence that the defendant is guilty, and you cannot consider this against the defendant in any way.” See Government’s Supplemental Appendix at 2. While the defendant does not challenge the sufficiency of the district court’s limiting instructions, it seems plain from Toner and Bisaccia that the lack of a proper purpose for admitting the guilty pleas to conspiracy charges is not cured by limiting instructions. As stated in Gullo, “[i]t is the general rule of this Circuit that while the evidence of a guilty plea by a co-conspirator is not admissible, under some circumstances, curative instructions are adequate to remove the harm where the pleas are to substantive counts.” United States v. Gullo, 502 F.2d 759, 761 (3rd Cir.1974) (citations omitted) (emphasis added). In this case, the admitted guilty pleas were to the charge of conspiracy, and the other crimes charged were the substantial acts of that conspiracy. This Court has long recognized the special significance of admitting evidence of a co-conspirator’s guilty plea to a conspiracy charge:
The guilty plea to a conspiracy charge carries with it more poténtial harm to the defendant on trial because the crime by definition requires the participation of another. The jury could not fail to appreciate the significance of this and would realize ... that it “takes two to tango.” A plea by a co-conspirator thus presents a unique situation which may require the courts to scrutinize more closely the purported remedial effects of instructions to the jury.
Gullo, 502 F.2d at 761. In the absence of a proper purpose for the admission of the guilty pleas, the curative instructions of the district court were not sufficient to remove the prejudice to Thomas presented by the evidence of his co-conspirators’s guilty pleas oh conspiracy charges.
The defense clearly stated to the court during the colloquy on its motion in limine that it had no intention of asking any questions about Thomas’s co-conspirators’s guilty pleas if its motion was granted. As Thomas’s intent was a central issue in the case, defense counsel argued that the introduction of the co-conspirators’s guilty pleas and any testimony about their intent to conspire to steal government property would seriously prejudice Thomas’s case. The credibility concerns cited by the district court in justifying its admission of the pleas were irrelevant, and the limiting instructions given were therefore inadequate to remove the prejudice caused in this instance. To uphold the admission of guilty pleas under these circumstances would thus effectively strip the Toner line of cases of any meaning.
Finally, the government argues that the admission of the guilty pleas was harmless error due to the overwhelming evidence at trial of Thomas’s guilt. Errors committed by a district court in a criminal case are considered harmless if the reviewing court *1207determines that there is a “high probability” that the error did not affect substantial rights. United States v. Werme, 939 F.2d 108, 116-17 (3d Cir.1991). Under this standard, a reviewing court must have “a sure conviction that the error did not prejudice the defendant, but need not disprove every reasonable possibility of prejudice.” United States v. Jannotti, 729 F.2d 213, 219-20 (3d Cir.1984).
It is a long-standing rule of this Circuit that evidence of a co-conspirator’s guilty plea is inadmissible to prove the guilt of one charged with conspiracy because a defendant has “a right to have his guilt or innocence determined by the evidence' presented against him, not by what has happened with regard to a criminal prosecution against someone else.” United States v. Toner, 173 F.2d 140, 142 (3d Cir.1949). In Bisaccia v. Attorney Gen. of N.J., 623 F.2d 307, 313 (3d Cir.1980), cert. denied, 449 U.S. 1042, 101 S.Ct. 622, 66 L.Ed.2d 504 (1980), this Court held that the admission of a co-conspirator’s guilty plea without limiting instructions from the trial judge combined with the prosecutor’s emphasis on the guilty plea as evidence of the conspiracy “so exceeded the tolerable level of ordinary trial error as to amount to a denial of constitutional due process.” The law of this Circuit clearly recognizes that substantial prejudice to a defendant’s rights can occur where evidence of a co-conspirator’s guilty plea is admitted. See United States v. Tyler, 878 F.2d 753, 760-61 (3d Cir.1989); United States v. Newman, 490 F.2d 139, 143 (3d Cir.1974).
In fact, most of the evidence submitted by the government was related to the shipment and storage of the parts; there was no direct evidence of Thomas’s criminal intent and most of the circumstantial evidence of his intent was credibly contested by Thomas. We are not left with the requisite “sure conviction that the error did not prejudice the defendant,” and do not conclude that the admission of Thomas’s co-eonspirators’s guilty pleas was harmless error. See United States v. Jannotti, 729 F.2d 213, 219-20 (3d Cir.1984).
V.
For all the reasons stated above, the introduction at trial of evidence of Thomas’s eo-conspirators’s guilty pleas was reversible error. We will reverse the judgment of conviction.
. If defense counsel should then have attempted to raise an inference on cross-examination that Thomas was being unfairly singled out for prosecution, additional remedial steps could have been taken.