Defendant assigns as error Judge Snepp’s ruling that defendant had the mental capacity to stand trial.
 Pursuant to motion of defense counsel, a pretrial hearing to determine defendant’s competency to stand trial was conducted on 2 September 1975. At this hearing, defendant’s mother, Eunice Taylor, and his father, Willie James Taylor, testified as to defendant’s unusual and strange behavior for a period of about two years preceding the hearing. Their testimony at this time was consistent with their testimony offered at trial in defendant’s behalf as related in our statement of facts. Both of these witnesses additionally testified that in his and her respective opinions their son did not understand the nature of these proceedings and was not able to assist counsel in presenting his defense.
Dr. Mildred Keene’s testimony at this hearing was in essence consonant with her testimony at trial as summarized in our statement of facts. She did not give an opinion as to whether defendant was mentally competent to stand trial.
Dr. Robert D. Cox, an expert in the field of psychiatry, stated that he treated defendant during September 1974. In his opinion, defendant’s unusual behavior “was most likely a drug-induced psychosis.” He related that defendant’s condition “cleared up” over a period of about three weeks when he was treated with an anti-psychotic drug called Haldon. Dr. Cox gave no opinion as to defendant’s competency to stand trial.
Dr. James Gregg Groce, after testifying to facts substantially in accord with his testimony at trial as summarized in our statement of facts, stated:
... I believe he can assist you in that he was able to relate to me fairly fully, and at times including trivial *227detail, what was going on at the time and his thinking at the time, his actions at the time, and I feel that that is the most important part of assisting you in his defense. He does have difficulty with his thinking but I don’t feel that it is so severe that he would be unable to participate in the preparation of his defense.
Defendant testified that he knew that he was accused of murder and that he was going to be tried for it. He said that he was able to help his lawyer and “could talk to you [his counsel] today and tomorrow about what happened on 24 January 1975, so that you [counsel] will understand it.”
Judge Snepp, after finding facts consistent with the evidence, concluded that defendant had capacity to proceed within the meaning of G.S. 15A-1001 and thereupon ordered the Sheriff of Mecklenburg County “to take especial care that the medications prescribed for the defendant are administered as directed and that the defendant actually take such medications.” G.S. 15A-1003, in part, provides:
(a) If a defendant is found to be incapable of proceeding, the court must enter an order directing the initiation of proceedings for judicial hospitalization, and the court’s order is a sufficient basis for the initation of those proceedings.
The test of a defendant’s mental capacity to stand trial is whether he has, at the time of trial, the mental capacity to comprehend his position, to understand the nature and object of the proceedings against him, to conduct his defense in a rational manner, and to cooperate with his counsel to the end that any available defense may be interposed. State v. Jones, 278 N.C. 259, 179 S.E. 2d 433; State v. Propst, 274 N.C. 62, 161 S.E. 2d 560; State v. Sullivan, 229 N.C. 251, 49 S.E. 2d 458; Strong, N. C. Index 2d, Criminal Law, § 29; 21 AM. JUR. 2d, Criminal Law, § 65. When, as here, this question is properly raised before the defendant pleads to the indictment, it should be determined prior to the commencement of the trial, as was done in this instance. State v. Propst, supra, at page 69. It may be determined by the trial court with or with*228out the aid of a jury. State v. Propst, supra, at page 68. When the court, as here, conducts the inquiry without a jury, the court’s findings of fact, if supported by evidence, are conclusive on appeal. State v. Squires, 265 N.C. 388, 144 S.E. 2d 49. . . .
In instant case, Dr. Groce, an expert in psychiatry, unequivocally stated that in his opinion defendant would be able to assist counsel in the preparation of his defense. Defendant testified that he was aware of the nature of the charges against him, and that he could talk to his counsel from day to day so that counsel could understand the happenings of 24 January 1975. The other expert witnesses did not contradict the crucial opinion given by Dr. Groce and, in fact, the only contradiction of Dr. Groce’s expert opinion came from defendant’s mother and father. We hold that the court’s findings of fact were supported by the evidence and the findings in turn supported Judge Snepp’s conclusions and ruling that defendant had the capacity to proceed within the meaning of G.S. 15A-1001 et seq.
Defendant next assigns as error the overruling of his objection to the admission of certain portions of Dr. Groce’s expert opinion. He first challenges the form of the following hypothetical question:
Dr. Groce, let me ask you a question. If the jury should find as the following facts: One, that the defendant joined with two other persons to travel to another location, that he carried a large and heavy weapon in a concealed manner, that he wore clothes especially to conceal the weapon, that he provided a wig to conceal the identity of a partner, that he attempted to commit an armed robbery, that he warned a storekeeper, “Don’t do anything foolish,” that he fired a single-shot weapon then fled because the storekeeper was armed, that he threw down the weapon and left the clothes used to conceal it, that he concealed himself in a nearby mill, that he asked directions calmly how to escape, that he took off identifying clothes, that he left a get-a-way car in a remote location, that he answered questions of another as to what he had done and why, and that he concealed himself until the following day, do you have an opinion satisfactory to yourself, based upon your medical knowledge and experience, as to whether or not the defendant could or might have had the capacity to *229distinguish between right and wrong at the time of, and in respect to the matter under investigation?
[2, 3] Expert testimony may be presented to the jury through the testimony of an expert based on his own personal knowledge and observation or through testimony of an expert based on a hypothetical question addressed to him in which the pertinent facts are assumed to be true, or rather, assumed to be found by the jury. State v. David, 222 N.C. 242, 22 S.E. 2d 633. However, a hypothetical question should include only facts supported by the evidence already introduced or those facts which a jury might logically infer therefrom. Questions should not contain repetitious, slanted or argumentative words or phrases. Petree v. Duke Power Co., 268 N.C. 419, 150 S.E. 2d 749; Ingram v. McCuiston, 261 N.C. 392, 134 S.E. 2d 705; 3 Strong, North Carolina Index 2d, Evidence § 49 at 681.
 Defendant first argues that the hypothetical question erroneously assumed that defendant concealed a weapon under a coat worn for that purpose and that defendant provided a wig to conceal the identity of an accomplice. The State’s witness Dennis Weathers, who drove defendant to the scene of the crime, stated that defendant wore a coat over his sweater and that he did not see a shotgun. He testified that as Taylor left the car, he put his hand in his coat “as if indicating he was holding some kind of weapon.” Weathers further testified that when defendant returned to the car, he said that he "had shot a woman with a shotgun and “he had it under his coat all the time.” This evidence would be sufficient for the jury to logically infer that defendant wore the coat for the purpose of concealing the shotgun. Admittedly there was no evidence in the record at the time the hypothetical question was asked concerning the provision of a wig to conceal the identity of an accomplice. We have held that the incorporation into a hypothetical question of an assumed finding as to a vital fact of which there was no evidence is ground for a new trial. State v. Simpson, 244 N.C. 325, 93 S.E. 2d 425. In our opinion, the erroneous assumption as to the furnishing of a wig to an accomplice by defendant in the hypothetical question was not of such vital nature as to require a new trial.
 Defendant further attacks the form of the hypothetical question on the ground that it made no reference to defendant’s extensive history of mental illness and to his prior judicial commitments.
*230  The general rule is that a hypothetical question which omits any reference to a fact which goes to the essence of the case and therefore presents a state of facts so incomplete that an opinion based on it would be obviously unreliable is improper and the expert’s answer to such a question will be excluded. However, it is not necessary to include in the hypothetical question all the evidence bearing upon the fact to be proved. The adversary has the right to present other phases of the evidence in counter-hypothetical questions so as to supply omitted facts and to ask the expert on cross-examination if his opinion would have been modified by the inclusion of such omitted facts. Dean v. Coach Co., 287 N.C. 515, 215 S.E. 2d 89; State v. Stewart, 156 N.C. 636, 72 S.E. 193.
 We concede that the challenged hypothetical question was not a model question, however, the deficiencies in the form of the question do not constitute reversible error.
 Defendant next assigns as error the rulings of the trial judge admitting into evidence defendant’s in-custody statements.
When the State offered Officer Crowell’s testimony concerning an inculpatory statement made to him by defendant, counsel for defendant objected and the trial judge then properly conducted a voir dire hearing in the absence of the jury to determine the admissibility of the evidence. Defendant concedes that the voir dire hearing was properly conducted, that the warnings required by Miranda v. Arizona, 384 U.S. 436, 16 L.Ed. 2d 694, 86 S.Ct. 1602, and a host of our own decisions were properly given. In this connection, Officer Crowell, on his direct examination, testified that at the time he gave defendant the warnings and during the period of interrogation “He was completely rational, seemed to be. . . . [T]he defendant appeared to understand what I was talking about during the time I was talking to him. He was coherent in his answers that he gave to me when I asked him questions. The answers that he gave me were responsive to the questions that I asked him.” Officer Crowell was the sole voir dire witness and his testimony was entirely in accord with the above-quoted direct testimony. At the conclusion of the testimony, the trial judge, inter alia, concluded:
. . . [T]hat said verbal warning of his Miranda rights and his written Waiver of Right to Remain Silent and Right to Counsel During Interview were understanding^ and *231voluntarily given and the defendant was under no compulsion to either answer in the affirmative as to his understanding of his constitutional rights or as to his signature on the Waiver of Right to Remain Silent and Right to Counsel During Interview, and the Court therefore concludes that any statements made by the defendant to the investigating officers was voluntary.
Defendant, however, relying on State v. Thompson, 287 N.C. 303, 214 S.E. 2d 742, contends that the trial judge failed to consider the entire record in his determination of the volun-tariness of defendant’s in-custody statements. In Thompson, we said:
. . . [T]here was ample evidence that the procedural safeguards required by Miranda were employed by the officers upon the taking of the statements from defendant. Nevertheless, we must still determine whether, under all of the surrounding circumstances, defendant voluntarily and understandingly made the inculpatory statements.
* * *
The fact that the defendant was youthful and that he made the challenged statements in the presence of police officers does not render the statements inadmissible, absent mistreatment or coercion by the officers. State v. Lynch, 279 N.C. 1, 181 S.E. 2d 561; State v. Murry, 277 N.C. 197, 176 S.E. 2d 738. Neither does a subnormal mentality, standing alone, render a confession incompetent if it is in all other respects voluntarily and understandingly made. If a person has the mental capacity to testify and to understand the meaning and effect of statements made by him, he possesses sufficient mentality to make a confession. Nevertheless, his mental capacity, or his lack of it, is an important factor to be considered in determining the volun-tariness of a confession. . . .
Dr. Groce testified that, in his opinion, defendant knew the difference between right and wrong on 24 January 1975. Dr. Mildred Keene who testified that defendant suffered from schizophrenia, paranoid type, also stated that on the occasions that she observed defendant he seemed to be oriented as to time, place and person. Further, she was of the opinion that defendant might be oriented on one day and disoriented on the next day.
*232Diagnosis of a defendant’s mental condition as being schizophrenia, paranoid type, does not, standing alone, excuse him from legal responsibility for his criminal conduct. State v. Potter, 285 N.C. 238, 204 S.E. 2d 649. The above-summarized medical testimony bears upon whether defendant could have understandingly and voluntarily made these challenged statements. In addition to the medical testimony, there was non-expert testimony concerning defendant’s ability to understand and relate at the time and place the inculpatory statements were made.
[8, 9] It is well recognized that á non-expert witness may testify as to his opinion of an accused’s mental condition when the witness has had reasonable opportunity to observe the person and form an opinion based on such observations. State v. Matthews, 226 N.C. 639, 39 S.E. 2d 819; State v. Nall, 211 N.C. 61, 188 S.E. 637; State v. Keaton, 205 N.C. 607, 172 S.E. 179. Officer Crowell had ample opportunity to observe and talk with defendant before, during and after the time the challenged statements were made. It is noted that Dr. Groce’s medical opinion related to 24 January 1975 and the non-expert testimony was based upon observations made on 25 January 1975. Further, we think it is significant that defendant’s sister who was present at the time the statements were made and who was called as a witness failed to testify that defendant appeared to be disoriented or that he did not appear to understand the warnings given him or the consequences of the statements that he made. Thus, the trial judge’s findings of fact were supported by the evidence and we are, therefore, conclusively bound by these findings. State v. Pruitt, 286 N.C. 442, 212 S.E. 2d 92; State v. Hines, 266 N.C. 1, 145 S.E. 2d 363. Neither do we find error in the fact that this evidence was admitted as a part of the State’s rebuttal evidence. Admission of evidence in rebuttal, even when the evidence is properly admissible in chief, rests within the trial judge’s sound discretion and his ruling thereon will not be disturbed absent a showing of gross abuse of that discretion. State v. Foster, 284 N.C. 259, 200 S.E. 2d 782; State v. Mack, 282 N.C. 334, 193 S.E. 2d 71. We hold that the trial judge did not err in admitting defendant’s in-custody statements as a part of the State’s rebuttal evidence.
 Defendant, relying upon Mullaney v. Wilbur, 421 U.S. 684, 44 L.Ed. 2d 508, 95 S.Ct. 1881, contends that the trial judge erred in instructing the jury that defendant had the burden of *233proving, to the satisfaction of the jury, that he was legally insane at the time the offense was committed. He further argues that the trial judge should have charged the jury that the State had the burden of proving beyond a reasonable doubt that defendant was sane at the time the offense was allegedly committed. These identical contentions were fully considered and rejected in the recent case of State v. Hammonds, 290 N.C. 1, 224 S.E. 2d 595. We reaffirm the reasoning and holding set forth in Hammonds. See also State v. Shepherd, 288 N.C. 346, 218 S.E. 2d 176.
 Finally, defendant contends that the court erred in denying his request to instruct the jury as to the provisions of G.S. 122-84.1.
In compliance with the provisions of G.S. 1-181 and before the judge began his instructions, defense counsel, inter alia, filed the following prayer for special instructions:
Request foe Jury Instruction
The Defendant respectfully requests this Court to charge the jury substantially as follows:
The provisions of North Carolina General Statutes, Section 122-84.1, copy of which is attached hereto and is incorporated herein by reference.
/s/ Paul L. Whitfield Attorney for Defendant
Sec. 122-84.1. Acquittal of defendant on grounds of mental illness; procedure.— (a) Upon the acquittal of any criminal defendant on grounds of mental illness, the trial court shall order the defendant held under appropriate restraint pending a hearing on the issue of whether the defendant is mentally ill and imminently dangerous to himself or others, as these terms are defined in Article 5A of this Chapter. The hearing shall be conducted in accordance with the provisions of G.S. 122-58.7 except that the hearing shall be held in a public courtroom and need not be closed to the public. Evidence adduced at the trial of the defendant on the criminal charges on the issue of mental illness shall be admissible at the hearing. If the hearing cannot be conducted prior to the termination of the ses*234sion of court in which the criminal trial was had, it shall be calendared in the district court in the same county within 10 days. If the court finds that the defendant-respondent is mentally ill and imminently dangerous to himself and others, it shall order him committed to a regional psychiatric facility designated by the Division of Mental Health Services for a period of not more than 90 days. The defendant shall thereafter be considered as though he had been committed initially under the provisions of Article 5A of this Chapter. If the court finds that the defendant is not mentally ill and imminently dangerous to himself or others, it shall order his discharge.
(b) The provisions of this section supersede those provisions of G.S. 122-84 which prescribe the procedures to be used in the case of a defendant acquitted of a criminal charge by reason of mental illness. (1973, c. 1437, s. 1.)
The trial judge did not instruct on the provisions of G.S. 122-84.1.
The question here presented is not a case of first impression. .In the case of State v. Bracy, 215 N.C. 248, 1 S.E. 2d 891, the defendant was indicted for first-degree murder. His counsel argued the provisions of the statute which provided for the detention of a defendant in a State hospital and his discharge on certain conditions following a verdict of not guilty by reason of insanity. On the other hand, the solicitor argued that defendant would go free if the jury returned a verdict of not guilty by reason of insanity. Neither made any objection to the other’s argument. Defense counsel requested the court to instruct according to his argument and his request was declined. On appeal, this Court found no error in the judge’s ruling and quoted, with approval, the following from State v. Matthews, 191 N.C. 378, 131 S.E. 743:
“. . . ‘The jury has fully discharged its duty, and performed its functions, under the law of this State, when its members have sat together, heard the evidence, a,nd rendered their verdict accordingly. As the judge must not invade the true office and province of the jury by giving an opinion in his charge, either in a civil or criminal action, as to whether a fact is fully or sufficiently proven (C.S., *235564), so the jury must be content to leave with the judge the grave responsibility imposed upon him to render a judgment, upon their verdict, according to law.’ ”
The identical question presented by this assignment of error was considered and decided in State v. Hammonds, supra. In Hammonds, the district attorney in his final argument to the jury told the jury that defendant would be back in his community if found not guilty by reason of insanity. The trial judge, without further elaboration, instructed the jury to disregard this remark. Prior to the court’s charge, defendant submitted a written prayer for instruction explaining the procedure for commitment in the event of an acquittal on the ground of insanity. Defendant duly excepted to the trial judge’s refusal to give the requested instructions. Justice Moore, speaking for a unanimous Court, after extensively reviewing the pertinent cases in this and other jurisdictions, in part, stated:
... To allow a jury to speculate on the fate of an accused if found insane at the time of the crime only heightens the possibility that the jurors will fall prey to their emotions and thereby return a verdict of guilty which will insure that defendant will be incarcerated for his own safety and the safety of the community at large. In the case before us, there could be no doubt in the jurors’ minds that defendant murdered Mr. Capel. There was considerable evidence that defendant was incapable of knowing right from wrong at the time he killed Mr. Capel, and also evidence that his mental condition would worsen with age. The jury’s questions on a recommendation of mercy indicate their sympathy for defendant’s condition. However, an overriding fear for the safety of the community could well have dictated their verdict in the absence of any information that defendant could be committed to a mental hospital if found not guilty by reason of insanity. The atmosphere was one of confusion and of uncertainty. To insure fairness to defendant and to get the trial back “on an even keel,” the trial judge, upon request by defendant, should have instructed the jury on the consequences of a verdict of not guilty by reason of insanity.
We hold, therefore, that, upon request, a defendant who interposes a defense of insanity to a criminal charge is entitled to an instruction by the trial judge setting out *236in substance the commitment procedures outlined in G.S. 122-84.1, applicable to acquittal by reason of mental illness. The failure to give such instruction in this case was prejudicial error, entitling defendant to a new trial. To the extent this opinion is in conflict with State v. Bracy, [215 N.C. 248, 1 S.E. 2d 891], that decision is modified. . . . (Emphasis ours.)
The holding in Hammonds squarely controls this assignment of error and upon authority of that case, this assignment of error is sustained. For failure of the trial judge to give the requested instruction, there must be a