Kipling Key, the defendant, was convicted of first-degree murder1 in the El Paso County District Court. The court of appeals affirmed. People v. Key, 680 P.2d 1313 (Colo.App.1984). The court held that *320although one of the trial court’s jury instructions defining “after deliberation” was erroneous, the error was harmless beyond a reasonable doubt. We granted cer-tiorari and now affirm.
I.
Key was charged with the first-degree murder of James Shadday. Key admitted that he killed Shadday but maintained at trial that he acted in a hasty and impulsive manner in a fight with Shadday.2
Harold Duane Johnson, a friend of both Key and Shadday, was the prosecution’s chief witness. His testimony established the facts surrounding the homicide and also provided the jury with evidence about the relationship between Key and Shadday.
Johnson met Key and Shadday in November 1980, when the two men were sharing a room with Johnson’s younger brother, John, at the United States Army base at Fort Carson. Johnson was also in the Army at the time of the homicide but lived off the base. Shadday owned a four-wheel drive pickup truck and, according to Johnson, gave Key a set of keys to the vehicle. Johnson testified that Shadday and Key drove into the mountains on a weekly basis to practice target shooting with a two-shot .22 caliber derringer that Key kept, with Shadday’s approval, in the glove compartment of the truck. Johnson considered Key and Shadday to be good friends and stated that he had never seen them argue or fight. Prior to his death, however, Shadday had been assigned to another room in the barracks at the request of Key and Johnson’s brother. Shadday, according to Johnson, was upset at being asked to move.
Johnson testified that on Wednesday, May 13, 1981, he and Key went to a bar. During a discussion concerning Shadday’s truck, Key told Johnson: “I could take Jimmy Shadday up in the mountains and shoot him_ I could take the truck because I had been buying the truck from him....” Other evidence indicated that Key and Shadday had gone shopping for trucks that week but Key had been told by a salesman that he could not qualify for a loan. Johnson had not been alarmed by Key’s statement because he did not think Key was serious.
Johnson last saw the victim late in the afternoon on Thursday, May 14. The next day he saw his brother and Key driving on the base in Shadday’s truck. Key explained his possession of the victim’s vehicle to Johnson by telling him that Shad-day had gone AWOL (absent without official leave) after selling his truck to Key. On that same day, Key went to the dealership which sold the truck to Shadday and attempted to have the vehicle’s registration changed to his name so that he could take over the remaining payments. Later that evening, Key came to Johnson and confessed that he killed Shadday. Key told Johnson that he and Shadday had gone to the mountains to do some target shooting. He said that they began to argue about the room situation. During an ensuing fistfight, Key shot the victim four times in the head. Johnson testified that Key told him: “And he [Shadday] wouldn’t die, and I picked up a rock and mashed his head in, and he still wouldn’t die. So I took his truck and ran over his head, and he still wouldn’t die. And I got scared and drug him out in the woods.”
*321Shadday’s body was discovered by a jogger about noon on Friday, May 15, on Gold Camp Road outside of Colorado Springs. Shadday had four gunshot wounds, two to the front of his head and two to the back of his head. His skull had been crushed, and there were tire-track impressions across his forehead. Empty shell casings, a bloodied rock, and tread marks matching the tires on the victim’s truck were found in the immediate vicinity. A number of empty and half-filled beer bottles were also found in the area. The El Paso County coroner testified that Shadday died of a “massive cranial cerebral trauma ... with extrusion or squeezing out of most of the brain at the time of the death.”3 In the coroner’s opinion, the victim’s blood alcohol level of 0.127 indicated that he may have consumed about six or seven bottles of beer before his death.
The central issue at trial was whether Key killed Shadday after deliberation. Accordingly, in two separate instructions, the trial court instructed the jury on the meaning of deliberation. Instruction No. 14 provided:
The term “after deliberation” means not only intentionally but also that the decision to commit the act has been made after the exercise of reflection and judgment concerning the act. An act committed after deliberation is never one which has been committed in a hasty or impulsive manner.
Instruction No. 15 stated:
The element of deliberation is established by proof of the formed designed [sic] to kill, and length of time is not a determinative factor. The only time requirement for deliberation within the meaning of the first degree murder statute is an interval sufficient for one thought to follow another.
Instruction No. 17 required that the requisite culpable mental state of the defendant had to be proven beyond a reasonable doubt.
The trial court overruled Key’s objection to Instruction No. 15 and submitted the instructions to the jury. In the course of the jury’s deliberations, the jury sent a note to the trial judge stating: “Need additional explanation of deliberation.” The trial court replied that it could not give any further explanation other than what was already contained in the instructions. The jury found Key guilty of first-degree murder. His motion for a new trial was denied and he was sentenced to life imprisonment.
Key appealed, alleging that the trial court committed reversible error in giving Instruction No. 15. The court of appeals acknowledged that the second sentence of the challenged instruction included language that was rejected by this court in People v. Sneed, 183 Colo. 96, 514 P.2d 776 (1973), but held that under People v. Blair, 195 Colo. 462, 579 P.2d 1133 (1978), the error was harmless beyond a reasonable doubt because the evidence of deliberation was overwhelming.
II.
Key concedes that Instruction No. 14 is a correct statement of the law but argues that the second sentence of Instruction No. 15 contradicted the statutory definition of “after deliberation” and effectively lowered the prosecution’s burden of proving deliberation as an element of first-degree murder.
Section 18-3-102(l)(a), 8 C.R.S. (1978), provides that “[a] person commits the crime of murder in the first degree if ... [ajfter deliberation and with the intent to cause the death of a person other than himself, he causes the death of that person or of another person.” The term “after deliberation” is defined in section 18-3-101(3), 8 C.R.S. (1978), to mean “not only intentionally but also that the decision to commit the act has been made after the exercise of reflection and judgment concerning the act. An act committed after deliberation is never one which has been *322committed in a hasty or impulsive manner.” See People v. Bartowsheski, 661 P.2d 235, 242 (Colo.1983) (“[Wjhile deliberation requires that a design to kill precede the killing, the length of time required for deliberation need not be long.... What is required for the element of deliberation is that the decision to kill be made after the exercise of reflection and judgment concerning the act.”).
The language used in Instruction No. 15 — that deliberation requires only an “interval sufficient for one thought to follow another” — originated in Van Houton v. People, 22 Colo. 53, 43 P. 137 (1895). In Van Houton, the defendant appealed his first-degree murder conviction on the ground that the evidence was insufficient to establish deliberation and premeditation.4 We upheld the conviction, stating:
Time ... is not essential if there was a design and determination to kill formed in the mind of the defendant previous to or at the time the mortal wound was given. It matters not how short the interval, if it was sufficient for one thought to follow another, and the defendant actually formed the design to kill, and deliberated and premeditated upon such design before firing the fatal shot, this was sufficient to raise the crime to the highest grade known to the law.
Van Houton, 22 Colo, at 66, 43 P. at 142 (emphasis added). Trial courts incorporated this language into jury instructions which stated that premeditation and deliberation may occur in a time interval “sufficient for one thought to follow another,” and such instructions were approved by this court. See Hammil v. People, 145 Colo. 577, 361 P.2d 117, cert. denied, 368 U.S. 903, 82 S.Ct. 182, 7 L.Ed.2d 98 (1961).
However, in People v. Sneed, 183 Colo. 96, 514 P.2d 776 (1973), we disapproved of the Van Houton language. Sneed declared that the legislature intended to abandon the Van Houton definition of premeditation when it defined the culpable mental state of first-degree murder as “premeditated intent” and the culpable mental state of second-degree murder as “intentionally, but without premeditation.” We said:
In effect, by emphasizing that “premeditated intent” and “intentionally, but without premeditation” were different, and that premeditation required design before the act, it indicated deliberation and reflection were necessary to create the premeditated intent.
This means that between the forming of the intent to do the act and the act itself, an appreciable length of time must have elapsed to allow deliberation, reflection and judgment.... A premeditated act ... is never one which has been committed in a hasty or impulsive manner.
Sneed, 183 Colo. at 100, 514 P.2d at 778 (citations omitted).
Six months after Sneed was announced, the legislature amended the first-degree murder statute and defined “after deliberation” in terms substantially similar to those used by this court in its interpretation of the word “premeditation.” Compare Ch. 52, sec. 1, § 40-3-101, 1974 Colo.Sess.Laws 251, with Sneed, 183 Colo, at 100, 514 P.2d at 778. Thus, the General Assembly did not resurrect the Van Houton definition, although it had an opportunity to do so.
Our analysis of Van Houton, Sneed, and the series of statutory enactments defining the elements of first-degree murder lead us to the conclusion that the legislature ac*323cepted our holding in Sneed that the Van Houton instruction is incompatible with the legislatively mandated definition of “after deliberation.” Cf. Music City, Inc. v. Duncan’s Estate, 185 Colo. 245, 248, 523 P.2d 983, 985 (1974) (“[W]here a legislature reenacts or amends a statute and does not change a section previously interpreted by settled judicial construction, it must be concluded that the legislature has agreed with the judicial construction.”). Therefore, the trial court erred when it submitted Instruction No. 15 to the jury.
III.
Having concluded that Instruction No. 15 contains an erroneous definition of “after deliberation,” we must now consider whether that error was of constitutional magnitude and, if so, whether the error was harmless beyond a reasonable doubt.
Under the due process clause of the fourteenth amendment to the United States Constitution an accused may not be convicted of a criminal offense “except upon proof beyond a reasonable doubt of every fact necessary to constitute the crime with which he is charged.” In re Winship, 397 U.S. 358, 364, 90 S.Ct. 1068, 1072, 25 L.Ed.2d 368 (1970). The prosecution’s burden includes proving beyond a reasonable doubt that Key possessed the culpable mental state required by the applicable statute. People v. Mattas, 645 P.2d 254 (Colo.1982). It is the duty of the trial court to properly instruct the jury on all matters of law, and instructions which fail to correctly define the elements of an offense charged, so that the jury may decide whether they have been established beyond a reasonable doubt, are constitutionally deficient. Id.
We believe that Instruction No. 15 was constitutionally deficient. Standing alone, the instruction defined the essential element of “deliberation” in a manner inconsistent with section 18-3-101(3), 8 C.R.S. (1978), and Sneed, 183 Colo. at 96, 514 P.2d at 776. However, error of constitutional dimension does not require reversal if the error was harmless beyond a reasonable doubt. Chapman v. California, 386 U.S. 18, 87 S.Ct. 824, 17 L.Ed.2d 705 (1967); Graham v. People, 705 P.2d 505 (Colo.1985); People v. Myrick, 638 P.2d 34 (Colo.1981); People v. Blair, 195 Colo. 462, 579 P.2d 1133 (1978). In the context of an erroneous jury instruction on a culpable mental state, we have previously considered two factors to determine whether the error was harmless beyond a reasonable doubt. First, the court reviews the jury instructions as a whole to ascertain whether — despite the erroneous instruction — the jury must have found that the defendant acted with the required mental state. People v. Blair, 195 Colo. at 462, 579 P.2d at 1133. Second, we consider whether the evidence on the issue of mens rea was overwhelming. Id.
We do not believe that Instruction No. 15 permitted the jury to return a guilty verdict without finding that Key killed Shad-day “after deliberation,” as that term is defined in section 18-3-101(3), 8 C.R.S. (1978), and in Sneed, 183 Colo. at 96, 514 P.2d at 776. Instruction No. 14 defined “after deliberation” in terms identical to those contained in section 18-3-101(3). Instruction No. 18, the defendant’s theory of the case, also employed the statutory language defining “after deliberation.” The erroneous language in Instruction No. 15 did not so distort the definition of “after deliberation” in Instruction No. 14 that the prosecution was relieved of its burden of proving the mental culpability requirement of first-degree murder beyond a reasonable doubt.
Additionally, the evidence on the issue of deliberation was overwhelming. The evidence established that Key wanted a truck like Shadday’s but could not afford one. There was also evidence that Key was in the process of buying Shadday’s truck and had made several payments on the vehicle. The day before the killing, Key told Harold Johnson that he “could take Jimmy Shad-day up in the mountains and shoot him.... I could take the truck because I had been buying the truck from him....” Key did in fact go up to the mountains with Shad-*324day the following day. After a fight developed between the two men, Key shot Shad- . day four times in the head. The evidence indicated that Key used his two-shot derringer pistol to shoot Shadday.5 Thus, Key had to reload the pistol before firing the third and fourth shots. Shadday had four gunshot wounds, two to the front of his head and two to the back of his head. After shooting Shadday, Key, believing that Shadday was still alive, mashed his head in with a rock. Key next positioned Shadday beneath his truck and ran over his head. He then dragged Shadday into the trees. Before leaving, Key removed Shad-day’s wallet and identification from his body. The following day, Key was seen driving Shadday’s truck and said that Shad-day had sold it to him and had gone AWOL.
In our view, this evidence overwhelmingly demonstrates that Key killed Shadday after deliberation. The jury could have reasonably believed that Key had decided to kill Shadday as early as the day before the homicide, when Key told Johnson that he could take Shadday to the mountains, shoot him, and take his truck. The sequence of events in the mountains the next day also demonstrates deliberation under the test announced in Sneed, 183 Colo. at 96, 514 P.2d at 778. As we have stated, Sneed requires that an “appreciable” length of time must have elapsed between the forming of the intent to do the act and the act itself. Here, even assuming that Key fired the first two shots without deliberation, an appreciable period of time elapsed before the third and fourth shots. Another appreciable length of time elapsed between the fourth shot and the moment when Key began mashing in Shadday’s head with a rock. A final appreciable length of time elapsed between the time Key put down the rock, got into the truck, and drove over Shadday’s head. In each such period,. Key had sufficient time to deliberate whether to kill Shadday. There is no support in the record for Key’s contention that he killed Shadday in a hasty or impulsive manner. Accordingly, the error in Instruction No. 15 was harmless beyond a reasonable doubt.
The judgment of the court of appeals is affirmed.
LOHR, J., dissents, and QUINN, C.J., joins in the dissent. NEIGHBORS, J., dissents, and QUINN, C.J., and LOHR, J., join in the dissent.. § 18-3-102(l)(a), 8 C.R.S. (1978).
. The defendant rested without calling any witnesses to testify on his behalf. The trial court gave the following jury instruction tendered by the defendant:
Instruction No. 18. It is the contention of the defense in this case that Kipling Key is not guilty of the offense of Murder in the First Degree, but is, instead, guilty of Manslaughter. The defense admits that Kipling Key killed the victim but contends that the killing was not "after deliberation” because the evidence has not shown beyond a reasonable doubt that Key made a decision to kill the. victim after the exercise of reflection and judgment concerning the act. The defense claims that the evidence shows instead that the killing was committed in a hasty and impulsive manner, provoked by an argument and fight with the victim.
If, after considering all of the evidence, you have a reasonable doubt that the killing was committed after deliberation, your verdict must be not guilty of Murder in the First Degree.
. The coroner testified that he conducted several tests on the body at 5:38 p.m. on May 15. The results of these tests indicated that the victim died ten to twenty hours earlier, or between approximately 9:30 p.m. on May 14 and 7:30 a.m. on May 15.
. In 1895, the murder statute, in pertinent part, provided:
Malice shall be implied when no considerable provocation appears, or when all circumstances of the killing show an abandoned and malignant heart. All murder which shall be perpetrated by means of poison, or lying in wait, torture, or by any kind of wilful, deliberate and premeditated killing; ... or perpetrated from a deliberate and premeditated design, unlawfully and maliciously, to effect the death of any human being other than him who is killed; or perpetrated by any act greatly dangerous to the lives of others, and indicating a depraved mind regardless of human life, shall be deemed murder of the first degree, and all other kinds of murder shall be deemed murder of the second degree.... 1 Mills’ An. Statutes, sec. 1176.
Van Houton, 22 Colo, at 65-66, 43 P. at 142.
. As we have noted, Johnson testified that Key kept the derringer in Shadday’s truck, and it was this weapon that the two men used to practice target shooting on a weekly basis. Although Key did not tell Johnson what weapon he used to shoot Shadday, Key did say that the purpose of the May 14 trip to the mountains was to go target shooting. Further, the El Paso County coroner testified that the bullet holes in Shadday’s head were “consistent with the low caliber slug_ And often a .22 caliber bullet will often allow you to survive for a while_”