delivered the opinion of the court:
This is an appeal by defendant from a 1985 conviction by a trial court in a bench trial finding defendant guilty of voluntary manslaughter and concealment. Defendant was sentenced on July 16, 1985, for 15 years on the manslaughter conviction and three years on the concealment conviction. Both sentences were to run concurrent.
The public defender of Cook County represented defendant at the trial and initially in this appeal. The public defender of Cook County filed a motion to withdraw as appellate counsel, determining that there was no issue of merit. This court then appointed the State appellate defender to represent defendant in this appeal.
There are suggestions in the record that promises by an assistant State’s Attorney were made that psychiatric help would be obtained for defendant if his mother, sister and brother-in-law would testify before the grand jury. On the other hand, the appellate defender raises only two issues on appeal. They are:
(1) That Kirkman (defendant) did not exhibit an intent to conceal the deceased homicidal death and therefore the conviction should be reversed; and
(2) Whether where the deceased attacked Kirkman with a knife while voicing her intent to kill him, William Kirkman was justified in using deadly force to defend himself.
The issue of unfulfilled promises by the assistant State’s Attorney was first raised by defendant’s trial counsel in a motion to quash *108the grand jury proceedings and to exclude testimony. At the hearing on the motion to quash, the assistant State’s Attorney testified, in part, as follows:
“Q. Now during the course of your interviews with the defendant’s mother, his sister and brother-in-law, did you ever make any promises to him concerning this case?
A. No, I did not.
Q. Specifically, sir, did [you] ever make any representations to them concerning the sanity or psychological well being of the defendant as you knew it to be on that date?
A. No.
* * *
Q. How did you respond when she asked you if the defendant would be allowed to plead guilty to insanity?
A. Mrs. McCloud asked me if her son could plead guilty to insanity and get some help, that he needed help. I told her that what his defense would be was up to his lawyer. Although I did tell her it sounded like he needed help.”
Based on this and other testimony, the trial court order denied Kirk-man’s motion to quash.
The psychiatric report in response to a trial court order concludes:
“Overall, the intellectual pattern that emerges is an unreflective, action-oriented person whose judgment is poor, whose intellectual development is weak, but whose grasp of social situations is not severely impaired.”
The State has had no opportunity to address this issue on appeal.
Finally, if, in fact, the issue is error tainting the trial, it is one that the proper administration of justice impels its determination by a full hearing rather than by being addressed sua sponte by an appellate court. Our post-conviction remedy contemplates such a hearing if an error rises to a constitutional level. Ill. Rev. Stat. 1985, ch. 38, par. 122 — 1 et seq.
On the issues that have been raised by defendant and responded to by the State, we affirm for the following reasons.
At trial the evidence presented, primarily through stipulation, established that defendant and the victim, Harriet Price, had been dating for several months, and that defendant was living with the victim and her mother. Although the relationship between defendant and the victim had allegedly ended, defendant was still living with her. On the evening of January 13, 1984, the victim was home with defendant and her two girl friends, Carol Frazier and Katherine Col*109lins. The victim and defendant began to argue, and when she asked defendant to leave, he refused. As she started to call the police, defendant hit the victim in the face, causing her to fall to the floor. Defendant then left. Shortly after this incident, the victim and her two friends went out and did not return home until 5 a.m. the next day. At that time defendant was speaking on the telephone with his mother, Deloyce Kirkman. The victim spoke with defendant’s mother and agreed to meet her at the latter’s house later that day.
At 1 p.m. the victim went to meet Deloyce Kirkman, but when she arrived at the house, defendant was the only one there. She then began arguing with him, and at one point she asked defendant to bring her a glass of water. Defendant refused and told the victim to get it herself.
According to the testimony of Glen McCloud, who is defendant’s brother-in-law and who recounted what defendant had told him about the incident, the victim came back from the kitchen with a knife and threatened to stab defendant. The victim was 4 feet 11 inches tall and weighed 118 pounds; defendant was 6 feet tall and weighed 145 pounds. As the victim came toward him with the knife, defendant grabbed her around the throat allegedly in self-defense. Shortly thereafter her knees buckled and she fell to the floor. Defendant then realized that he had killed her.
Deloyce Kirkman worked at a bar on the first floor of the building where she lived. Aboiit 4 p.m. on the day of the occurrence she went to her apartment and found that an ashtray and game were on the floor and that a table was out of place. Defendant was in the bathroom with the water running. When Deloyce Kirkman asked about the condition of the apartment, defendant replied that he tripped when he went to answer the door.
At 7 p.m. defendant contacted McCloud, went to his house and told him that he had killed the victim. He described the events leading up to her death and told McCloud that the victim’s body was under the stairway of his mother’s house. McCloud reported defendant’s conversation to Deloyce Kirkman, who then called the victim’s house, but found no one at home. She then took a flashlight and used it to illuminate the darkened stairway where the victim’s body was allegedly hidden, but saw nothing. McCloud then found defendant and accused him of fabricating the story of victim’s death. Defendant stated he had no reason to lie and that the victim’s body was under the steps. Sometime later, defendant told Deloyce Kirkman that he had killed the victim, placed her body in a laundry bag and placed it behind the stairway.
*110At 7 a.m. the next day, defendant asked McCloud to help him flee. McCloud refused, stating that he did not believe defendant’s story because he could not find a body. Defendant continued to insist that the body was where he originally said it was. Deloyce Kirkman, who had been calling the victim's residence attempting to locate her, at this time called the police. At 10:30 a.m. Deloyce Kirkman went down the stairway and found the victim’s body. Officer Rivera arrived at 1 p.m., was shown the victim’s body and contacted additional officers. Shortly thereafter, defendant called his mother from his stepmother’s house, and Officer Rivera was informed of defendant’s location. Officers Guiffre and Nakutis subsequently arrested defendant at this location.
The pathologist’s testimony was also presented by stipulation. His examination of the victim revealed a number of abrasions to her head, face, neck, chest and back. He also found that her left neck bone was fractured, and that the cause of death was strangulation.
As indicated above, defendant brings this appeal, contending only that the evidence did not support his conviction for concealment of a homicidal death and that his conviction for voluntary manslaughter was also improper because he killed the victim in self-defense.
I
Concealment of a homicidal death is governed by section 9— 3.1 of the Criminal Code of 1961 (Ill. Rev. Stat. 1983, ch. 38, par. 9 — 3.1) which states:
“(a) A person commits the offense of concealment of homicidal death when he conceals the death of any other person with knowledge that such other person has died by homicidal means.”
In order to establish that the offense of concealing a homicidal death has occurred, the evidence must show that a homicide has occurred, that the defendant knew both the fact and cause of death and that defendant took affirmative steps to conceal the homicide with the specific purposes of preventing or delaying its discovery. (People v. Stiles (1977), 46 Ill. App. 3d 359, 360 N.E.2d 1217.) Concealment of a homicidal death includes situations where the homicidal nature of the death or the body itself is concealed. People v. Vath (1976), 38 Ill. App. 3d 389, 347 N.E.2d 813.
In the instant case a homicide occurred when the victim was strangled by defendant, and defendant revealed his knowledge of the fact and cause of the victim’s death when he first informed his brother-in-law that he had killed her. Defendant also took affirmative *111action and intentionally concealed the victim’s body when he placed it in a laundry bag and hid the body from view.
Defendant argues that he should not have been convicted of concealing a homicidal death because he made no attempt to conceal the fact of the victim’s death, and in fact, facilitated the discovery of her body. Although defendant did inform his family of the circumstances of the victim’s death, he intentionally concealed her body, and only moved it to a location where it could be discovered when defendant’s brother-in-law stated that he did not believe defendant’s story because he could not find the body. Even though a defendant may reveal the location of a victim’s body several days after the homicide has occurred, the initial concealment of the victim’s body constitutes an offense. People v. Mueller (1985), 130 Ill. App. 3d 385, 474 N.E.2d 434.
For these reasons, we find that defendant’s conviction for the concealment of homicidal death was proper.
II
Both the offense of voluntary manslaughter under section 9 — 2(b) of the Criminal Code (Ill. Rev. Stat. 1983, ch. 38, par. 9 — 2(b)) and self-defense under section 7 — 1 of the Criminal Code (Ill. Rev. Stat. 1983, ch. 38, par. 7 — 1) involve the issue of whether a defendant subjectively believed that force was justified for his self protection. Once there is a finding that defendant believed force was justified, the next determination is whether or not defendant’s belief is found to be reasonable. Once it is found to be unreasonable, a conviction for voluntary manslaughter results. (People v. O’Neal (1984), 104 Ill. 2d 399, 472 N.E.2d 441.) In order to establish self-defense, defendant must show that unlawful force was threatened against him, that he was not the aggressor, and that the amount of force used was necessary to protect himself from imminent harm. People v. Jordan (1985), 130 Ill. App. 3d 810, 474 N.E.2d 1283.
Defendant was the only witness to the altercation between himself and the victim that resulted in her death. He claims that the victim threatened him with unlawful force when she came after him with a knife, and that the force he used was necessary to protect himself against this imminent harm. The trier of fact determines the credibility of the witnesses and the weight of their testimony. (People v. Foster (1979), 76 Ill. 2d 365, 392 N.E.2d 6.) In the instant case, the trial court considered the evidence and found defendant’s belief that he had to use deadly force was unreasonable. A reviewing court will not alter the determination of a trier of fact unless the evidence *112justifies a reasonable doubt of guilt. (People v. Jordan (1985), 130 Ill. App. 3d 810, 474 N.E.2d 1283.) We conclude that the evidence corroborated the fact that defendant used more force than was necessary for his own self-defense where he was over one foot taller and 27 pounds heavier than the victim and exerted such force that he fractured a neck bone when he strangled her to death. Therefore, the trial court properly found defendant guilty of voluntary manslaughter.
Accordingly, the judgment of the circuit court is affirmed.
Affirmed.
LORENZ, P.J., concurs.