Eddie Turquitt was convicted by a jury on all four counts of an indictment charging him with unlawful possession of stolen mail matter, knowing the same to have been stolen, in violation of Title 18, U.S.C., Section 1708. He was adjudged guilty and given a general sentence of three years imprisonment and fined $1000, to stand committed until payment of the fine. This appeal rests upon two contentions. Appellant initially argues that the court improperly received evidence, over objection, of a past criminal act for which he had been neither charged nor convicted. He also claims that “plain error”, Rule 52(b) F.R. Crim.P., resulted when the trial judge failed to give the jury a cautionary instruction as to remarks made by governmental counsel in his closing argument. We reverse on the first ground.

The government established, partly by testimony and partly by stipulation, that during a thirty day period four checks were stolen from the United States Mails in Birmingham, Alabama. There was testimony that the checks were cashed at Birmingham banks, and that the endorsements on them were forged.^[1] The government produced an expert handwriting/fingerprint analyst, James DeYoung, who testified that he could positively state that the endorsements on two^[2] of the four checks were written by the appellant. Although noting “some suspicious agreement” between the endorsements on the other checks and the appellant’s handwriting samples, DeYoung stated that some features were present that he could not account for, and that he was unable positively to identify as appellant’s the endorsement on those checks. DeYoung testified further that he found appellant’s fingerprints on three of the four checks in question, and on some deposit slips and additional checks received in evidence.

Appellant Turquitt testified in his own defense. He denied any guilty knowledge regarding the checks but stated that he possibly had touched some of the checks and deposit slips. He denied signing any of the checks or opening a checking account in the name of L. S. Boggan.^[3] Turquitt explained that while he was at the home of Raul Vella, a former employee of Turquitt Masonry Company, Inc., Mr. Vella told him to look at some papers on a table. Appellant[*467] testified that he looked through these papers, a checkbook and some checks, and then put them back on the table. Raul Vella was later arrested on December 2, 1975, when he tried to cash the check payable to Schumate covered by Count IV of the indictment.^[4] It was Turquitt’s further direct testimony that a few days before Raul Vella was arrested, Mr. Vella handed him a check and asked him to cash it, which request he refused. He stated that he touched the check when Mr. Vella handed it to him, but denied signing the name of John L. Schumate on the back of the check.

On cross-examination, appellant was asked by government counsel where he lived from September 1975 through December 1975. Turquitt gave his address as the Arboretum Apartments in Hoover (Alabama), Apartment 1818C. Counsel then asked if he had ever lived at 917C Valley Avenue, and Turquitt denied ever living at that address. The next question was whether he had ever gone under the name of Eddie Von Blitzen. Turquitt denied this also. At this point, defense counsel objected to the line of inquiry, and when the prosecutor said he was “laying a predicate for the—” the trial judge overruled the objection. Appellant was then asked if he had ever signed a lease under the name of Eddie Von Blitzen. Turquitt denied ever doing so, and his attorney again objected. The objection was overruled.^[5] The lease and a rental application form, both bearing the signature of Edward Von Blitzen, were admitted into evidence over defense counsel’s continuing objection. Further cross-examination revealed that Gene Carter, appellant’s longtime friend and employee, lived in the apartment named in the lease signed “Edward Von Blitzen”.

On rebuttal, the government called as a witness, Shirley Ray, an employee of Tillman Realty. She stated that she had rented an apartment to Gene Carter and Edward Von Blitzen. When asked if Edward Von Blitzen was in the courtroom, she pointed to the appellant. She also testified that he had signed the lease. Defense counsel consistently objected to these questions.^[6] No limiting instructions were given[*468] by the trial court with respect to the “lease evidence”.

Appellant’s first ground of appeal is that the trial court erroneously admitted evidence of an unrelated criminal act, the “lease evidence”, indicating either forgery or signing of a lease under an assumed name, for which he had never been charged or convicted, solely for impeachment purposes. He claims that the “lease evidence” severely prejudiced his defense, and that he was deprived of a fair trial by its admission before the jury. The point is well taken and requires reversal of the judgment of conviction.

“[EJvidence which shows or tends to show commission of crimes not charged is inadmissible in a trial for a particular crime”, (citation omitted) United States v. Broadway, 477 F.2d 991, 994 (5th Cir. 1973). See also Weiss v. United States, 122 F.2d 675 (5th Cir. 1941), cert. denied, 314 U.S. 687, 62 S.Ct. 300, 86 L.Ed. 550 (1942). This rule is necessary to prevent conviction based on a jury belief that the accused is a person of bad character. The jury’s determination of guilt or innocence should be based on evidence relevant to the crime charged. This rule is of course subject to several exceptions. Evidence of the commission of other crimes, closely related both in time and nature to the crime charged, may be admissible if offered to prove an essential element of the charged offense, such as motive, intent, identity, guilty knowledge, or a common scheme, plan or design. See United States v. Crockett, 514 F.2d 64 (5th Cir. 1975); United States v. Broadway, supra; 2 C. Wright, Federal Practice & Procedure § 410 (1969).

In many cases, evidence of other crimes closely related in time and nature to the crime charged fit at least one of the exceptions to the rule. But evidence that the accused committed a prior criminal offense is inherently dangerous because of the likelihood that prejudice to the defendant may result from confusing the issues by leading the jury to infer that since the defendant has committed a similar crime, he must also have committed the crime for which he is on trial. See United States v. Goodwin, 492 F.2d 1141 (5th Cir. 1974). Cautionary instructions by the court may not curb the harmful effects. Because of the high risk of prejudice courts restrict the use of such evidence. Judicial inquiry does not end with a determination that the evidence of another crime is relevant and probative of a necessary element of the charged offense. It does not suffice simply to see if the evidence is capable of being fitted within an exception to the rule. Rather, a balancing test must be applied. The evidence of another similar crime must not only be relevant, it must also be reason[*469] ably necessary to the government’s case, United States v. Goodwin, supra, and it must be plain, clear, and conclusive, United States v. Broadway, supra, before its probative value will be held to outweigh its potential prejudicial effects. See United States v. Simmons, 503 F.2d 831, 835 (5th Cir. 1974).

The government primarily argues that the “lease evidence” in this case is not evidence of an act constituting a criminal offense. After examining Alabama’s forgery statute,^[7] we think that the appellant’s alleged signing of a false name to a lease clearly could be the basis for criminal charges under the laws of that state. We reject the government’s initial argument.

The United States also seeks to justify admission of the “lease evidence” by urging that it was offered to authenticate the handwriting of the defendant, and to bolster the handwriting expert’s credibility in identifying appellant’s writings. Government counsel claims that this evidence was probative in establishing possession of the Schumate (Count IV) check, possession being an essential element of the crime charged. The government’s reasoning in this respect is difficult to follow. It seems to be urging that because proof of possession depended in part on the ability of the handwriting expert to recognize and identify appellant’s handwriting, the “lease evidence” (the lease itself, the lease application, and the eyewitness testimony of Ms. Ray that she saw Turquitt sign those papers) is relevant to the element of possession. Rule 901(b)(3),^[8] Federal Rules of Evidence, is cited to support the admissibility of the “lease evidence”, as known handwriting specimens. The applicability of Rule[*470] 901 to this situation appears strained. In any event, other known and less prejudicial specimens would have achieved the same result. Since government exhibit 16 was a four page specimen of appellant’s admitted handwriting, it should have sufficed for comparison purposes. Cumulation in this respect was unnecessary, assuming the actual purpose was to provide an additional exemplar of Turquitt’s handwriting. In fact the expert’s credibility was never seriously jeopardized. His credentials were excellent and he explained his analysis of the handwriting and the fingerprint evidence thoroughly and with great care. The government has failed to show that this evidence was reasonably necessary to its case. The “lease evidence” failed to satisfy any of the recognized exceptions outlined by our decisions concerning evidence of pri- or criminal acts.^[9] The two crimes involved, forgery and possession of stolen mail matter bear little relationship one to another.^[10]

While it is largely within the trial court’s discretion to decide whether other crime evidence is admissible, either in chief or in rebuttal, Labiosa v. Canal Zone, 198 F.2d 282 (5th Cir. 1952), this discretion has definite limits. See United States v. Boyd, 446 F.2d 1267 (5th Cir. 1971). The trial court gave little consideration to balancing the need and probative value of the evidence against its possibly prejudicial effect. Our own assessment is that the potential for prejudice far outweighed any probative benefit to be derived by allowing the jury to consider the “lease evidence”. Its admission was in error.

Assuming (as the government argues) that the appellant’s act of signing a false name to the lease was not a crime under Alabama law, the “lease evidence” was still inadmissible because it was outside the scope of proper impeachment. The record indicates that the “lease evidence” was introduced solely for impeachment purposes. In his closing argument, government counsel stressed appellant’s lack of credibility as demonstrated by such evidence.^[11] Moreover, when defense counsel questioned the trial judge as to the court’s intended charge on the lease evidence, the judge indicated that the testimony was to be considered only as affecting appellant’s credibility as a witness.^[12] Turquitt took the stand in an effort to explain the presence of his fingerprints on the checks. His explanations tending to show that the fingerprints were of innocent origin might have created a reasonable doubt in the minds of the jurors as to whether he had participated in the offense charged.^[13] The effect of[*471] “lease evidence” might well have been to erase any such doubt from the minds of the iurors-

When an accused takes the stand as a witness he may be impeached as to character by cross-examination and rebuttal to the same extent as any other witness. United States v. Davenport, 449 F.2d 696 (5th Cir. 1971). But no witness may be impeached by evidence of any prior specific misconduct or crime for which he has not been convicted. See United States v. Cluck, 544 F.2d 195 (5th Cir. 1976); United States v. Davenport, supra; Hurst v. United States, 337 F.2d 678 (5th Cir. 1968).^[14]

Introduction of the lease and permitting Ms. Ray’s testimony was improper as extrinsic evidence of prior misconduct not culminating in a judgment of conviction.

Turquitt asserts additionally that error occurred when the trial court permitted the prosecutor to imply, in his closing argument to the jury, that the accused had a criminal record, and further argues that the trial court should have instructed the jury to draw no inference from the prosecutor’s remark. Assuming that this issue is not likely to arise at a later trial, we pretermit discussion of it.

CONCLUSION

The “lease evidence” was improperly admitted. It would be rank speculation to say that its receipt in evidence was “harmless beyond a reasonable doubt”, Chapman v. California, 386 U.S. 18, 87 S.Ct. 824, 17 L.Ed.2d 705 (1967). Without this evidence the jury may well have acquitted Turquitt. He is entitled to a new trial with the “lease evidence” excluded.

REVERSED.