Defendant appeals from his conviction by a jury of the crime of aggravated robbery, a first degree felony, Section 76-6-302, Utah Criminal Code. We reverse and remand for a new trial. All statutory references are to U.C.A.1953.
By information defendant was accused of using a deadly weapon or facsimile thereof, to wit, a revolver to rob Brenda Moore Bradley and Barbara Harris on June 30, 1975. In a bill of particulars the State alleged that defendant together with one Kenneth Douglas Wells, entered the residence of Barbara Harris and by use of a deadly weapon, a revolver robbed Harris and Bradley. Specifically the State alleged defendant, together with Wells, took from the person or immediate presence of Bradley, the approximate sum of $138, in cash; and the approximate sum of $180, from Harris in cash.
The evidence adduced by the State indicated that defendant and Wells entered the residence with guns and robbed not only Harris and Bradley but other persons also present. In addition, a .22 caliber pistol in the bedroom, hidden under a pillow, was also taken. Subsequently, defendant and Wells were apprehended in Tucson, Arizona. Wells was arrested, while seated in his automobile. The .22 caliber pistol was found in the vehicle. Defendant was found by the Tucson police in a hotel in the vicinity where Wells’ car was parked. Defendant was unconscious from an overdose of heroin.
Defendant called Wells as a witness. Defendant also testified substantially the same as did Wells. They both admitted going to the residence, which they described as a “dope house,” for the purpose of buying heroin. Defendant testified he had previously purchased drugs from Bradley. He stated that on this occasion Bradley informed him Harris had the drugs. He purchased drugs from Harris and paid her sixty dollars for two bags of heroin. Defendant immediately administered to himself one bag and gave the other to Wells. Defendant was of the opinion the narcotic was no good and engaged in an argument with Bradley concerning the quality of the merchandise.
Defendant testified that during the course of the argument he proclaimed he was tired of arguing. He removed a clear plastic bag containing balloons of heroin from a table, hailed his companion Wells, and the two departed. Defendant insisted he took only the heroin and that he had no firearms of any kind. The testimony of defense witness, Wells, coincided with defendant’s.
*1353Defendant contends that the trial court erred by permitting the .prosecution to present evidence not specifically described in the information or bill of particulars. Over defense counsel’s objection, the trial court allowed testimony involving other crimes committed on the premises at the time Harris and Bradley were robbed, viz., the crime charged in the information and bill of particulars. There was testimony that other individuals present on the premises were robbed and the .22 caliber pistol was taken from the bedroom.
A bill of particulars need not plead matters of evidence, Section 77-21-9(1) was designed to enable a defendant, where the short form information is used to have the stated particulars of the charge which he must meet. The bill of particulars was not intended as a device to compel the prosecution to give an accused person a preview of the evidence on which the State relies to sustain the charge.1
The testimony concerning the other allegedly criminal acts committed by defendant during the course of the commission of the crime with which he was charged, were, in fact, eyewitness descriptions of the events that occurred. If the State elects not to charge an accused with the additional crimes, this is not a ground to exclude testimony of those crimes that constituted an integral part of the acts committed by an accused during the course of the crime with which he is charged. Any attempt to segment the testimony of the witnesses herein would have seriously impaired their ability to relate to the jury their perception of the events as the drama unfolded. The State was not required to reveal this evidence in advance to defendant by means of the bill of particulars.
Defendant further contends there was prosecutorial misconduct in questioning defense witness, Wells, which constituted prejudicial error.
The prosecution witnesses had testified defendant and Wells had guns when they entered the premises. Before defendant and Wells vigorously denied they had such weapons at the time of the alleged commission of the crime, or thereafter during the time they were in Arizona.
In the cross-examination of witness Wells, the prosecutor queried about Wells’ ownership or possession of a gun. Wells responded in the negative to these questions. The prosecutor then asked: “you were arrested for armed robbery, doesn’t that mean you had a gun with you?”
An objection was asserted to this question, which was sustained by the court. The defendant moved for a mistrial on the ground that the questioning of Wells concerning his arrest in Arizona prejudiced defendant’s right to a fair trial. Defendant urged that the questioning violated Rule 55, U.R.E.
Under Rule 55, U.R.E., evidence that a person committed a crime on a specified occasion is admissible when relevant to prove some other material fact. Wells had specifically denied possession of a weapon and any evidence discrediting this denial was relevant to this issue. If the questioning and responses are reviewed within the context of the record, it is revealed that the cross-examination was directed towards the possession of a gun by Wells. The questioning was not for the purpose and did not have the effect of implicating either defendant or Wells with other crimes or to degrade them and give the jury the impression they had a propensity for crime. The sole purpose was to discredit their vigorous denial of knowledge or possession of weapons. The cases cited and relied upon by defendant are distinguishable.2
Defendant further contends the trial court erred by denying defense counsel upon cross-examination of victim, Bradley, the right to inquire whether she had used heroin on the date of the alleged robbery.
*1354Defendant cites and relies on Rule 20, U.R.E. and Section 78-24-1; the State relies on Rule 45, U.R.E.
Section 78-24-1, provides:
. although, in every case the credibility of the witness may be drawn in question, by the manner in which he testifies, by the character of his testimony, or by evidence affecting his character or truth, honesty or integrity, or by his motives, or by contradictory evidence;
Rule 20, U.R.E., provides:
Subject to Rules 21 and 22, for the purpose of impairing or supporting the credibility of a witness, any party including the party calling him may examine him and introduce extrinsic evidence concerning any statement or conduct by him and any other matter relevant upon the issues of credibility.
Rule 45, U.R.E., provides:
Except as in these rules otherwise provided, the judge may in his discretion exclude evidence if he finds that its probative value is substantially outweighed by the risk that its admission will (a) necessitate undue consumption of time, or (b) create substantial danger of undue prejudice or of confusing the issues or of misleading the jury, or (c) unfairly and harmfully surprise a party who has not had reasonable opportunity to anticipate that such evidence would be offered.
In State v. Mason3 this Court ruled it was within the legitimate scope of cross-examination to inquire whether a witness had been under the influence of a narcotic drug.
. it is within the scope of cross-examination of a witness to inquire as to anything which may reasonably be regarded as affecting the accuracy or credibility of his testimony. This includes matters which would test his ability to observe and understand, or his memory, or his capacity to adequately relate his knowledge of the facts. .
The record indicates a discrepancy in the testimony between witness Bradley and the witnesses Timms, viz, whether defendant and Wells had weapons when they entered, or acquired the .22 pistol later. Furthermore, an integral part of the defense was the claim the residence was a “dope house,” and the habitues were involved with narcotics. Under the circumstances of this case, the probative value of the excluded evidence outweighed any potential prejudice which might inure to the witness, and the trial court abused its discretion. Defendant was entitled to determine whether Bradley was under the influence of drugs and if so, the effect the narcotic might have had on her ability to perceive the facts.4
Finally, defendant contends the action of the trial court in excluding the testimony of a defense witness that he had purchased narcotics from witness, Harris, constituted prejudicial error.
Witness, Harris, testified she had never lied under oath and that she had not lied at the preliminary hearing, where she denied she had ever sold heroin. Defense counsel called as a witness, Darryle Riddle, who testified he had worked as an undercover agent for the police during September and November 1975. Mr. Riddle made undercover narcotics purchases as one of his duties. He testified he knew witness, Harris; at this point, the prosecution requested to voir dire the witness outside the presence of the jury.
The prosecution determined that Riddle was not engaged by the police on June 30, 1975, the day of the crime, and, therefore, objected to the testimony. Defense counsel made a proffer of the testimony of Riddle for the record, viz, he would testify he had purchased heroin from Harris at her residence on September 29 and October 2 or 3 of 1975. Defense counsel vigorously asserted he was entitled to impeach her statements that she had never sold heroin. Counsel pointed out his defense was based on the claim that no robbery occurred, but there was a theft of heroin. The prosecu*1355tion witnesses insisted there was no heroin, and defense counsel urged that to receive a fair trial, defendant was entitled to present evidence that Harris had, in fact, lied.
The State relies on the rule that the answers of a witness upon cross-examination on any irrelevant or collateral matter are conclusive and binding, and the witness may not be contradicted or impeached upon an immaterial or collateral matter of issue.5
What is a collateral matter or issue? It is generally stated that facts which would be independently provable are not collateral. Obviously, facts which are relevant to the issues of the case come within this category. In addition, facts independently provable to impeach or disqualify the witness, whether or not introduced to contradict him, are admissible. For example, testimony may be introduced to show bias, interest, conviction of a crime or lack of capacity or opportunity for knowledge of the facts related.
Finally, a third kind of fact must be considered. Suppose a witness has told a story of a transaction crucial to the controversy. To prove him wrong in some trivial detail of time, place, or circumstance is ‘collateral.’ But to prove untrue some facts recited by the witness that if he were really there and saw what he claims to have seen, he could not have been mistaken about, is a convincing kind of impeachment that the courts must make place for, although the contradiction evidence is otherwise inadmissible because it is collateral under the tests mentioned above. To disprove such a fact is to pull out the linchpin of the story. So we may recognize this third type of allowable contradiction, namely, the contradiction of any part of the witness’s account of the background and circumstances of a material transaction, which as a matter of human experience he would not have been mistaken about if his story were true.6
The proffered testimony of witness Riddle was not impeachment of witness, Harris, on a collateral issue. There were two versions as to what occurred at the Harris’ residence. According to the prosecution two armed robbers charged into the home, terrorized the occupants, and took cash from victims Harris and Bradley. Narcotics were not present or involved. According to the defense, no weapons were involved, no cash was taken, two dissatisfied customers stole a bag of narcotics as a culmination of an argument over the quality of the goods purchased. Whether Harris, in fact, distributed narcotics from her residence was, indeed, a relevant issue in the case, which defendant was entitled to prove for a purpose independent of impeaching Harris’ testimony; thus, it was not a collateral issue.7
Since this excluded evidence would probably have had a substantial influence in bringing about a different verdict, the judgment must be reversed.8 The defendant is entitled to an opportunity to present that evidence which tends to corroborate his version of the incident.
WILKINS and HALL, JJ., concur.. State v. Lack, 118 Utah 128, 134, 221 P.2d 852 (1950); State v. Winters, 16 Utah 2d 139, 396 P.2d 872 (1964); State v. Moraine, 25 Utah 2d 51, 475 P.2d 831 (1970).
. State v. Kazda, 14 Utah 2d 266, 382 P.2d 407 (1963); State v. Dickson, 12 Utah 2d 8, 361 P.2d 412 (1961).
. Utah, 530 P.2d 795, 797 (1975).
. Doe v. State, Alaska, 487 P.2d 47, 58 (1971).
. Davenport v. State, Alaska, 519 P.2d 452, 454 (1974).
. Id. pp. 454-455 of 519 P.2d.
. See State v. Harp, 13 Wash.App. 273, 534 P.2d 846, 849 (1975).
.Rule 5, U.R.E.