"28 A person is not criminally responsible for an act or omission if at the time of doing the act or making the omission he is in such a state of mental disease or natural mental infirmity as to deprive him of capacity to understand what he was doing or of capacity to control his actions or of capacity to know that he ought not to do the act or make the omission. A person whose mind at the time of his doing or omitting to do an act is affected by delusion on some specific matter or matters but who is not otherwise entitled to the benefit of the foregoing provisions of this section is criminally responsible for the act or omission to the same extent as if the real state of things has been such as was induced by the delusions to believe to exist." For an accused person to successfully rely on the first limb of section 28 of the Criminal Code supra, he must prove that at the time the offence was committed, he lacked: (a) the capacity to understand what he was doing (b) capacity to control his action (c) capacity to know that he should not do the act or make the omission. See Adegbesan v. The State (1986) 1 NSCC; Lake v. The State (1985) 1 SC, (1985) 1 NWLR (Pt. 1) 1 SC; Egbe Nkanu v. The State (1980) 3-4 SC 1; Udofia v. The State (1981) 11-12 SC 49. For the second limb of section 28 of the Criminal Code to avail an accused person as a defence, he must show that there is a set of facts which does not actually exist but which he imagines to exist, that as a result of his belief that the set of facts actually exists as he imagined them, he commits an act of omission or commission which has resulted in the charge on which he stands trial and that if those facts had existed as so imagined by him they would have amounted to a complete defence to his act which is called in question even though the factual situation was not real: see Anthony Ejinima v. State (1991) 6 NWLR (Pt. 200) 627 at 657. To appreciate the issues canvassed in this appeal, it is necessary to review the facts of the case. The evidence led at the trial revealed that in the morning of 5/2/87, Sunday Guobadia (PW3) the father of the appellant, ordered him and one Victor to go to the farm. The appellant and the said Victor proceeded to the farm on a bicycle with Victor conveying the appellant on the bicycle. Half way on their journey to the farm, the appellant changed his mind and decided to return home. While trekking home, (P.W.3) his father met him and tried to persuade him to go to the farm but this was to no avail. When the appellant finally got home, he met Rosaline Guobadia (P.W2) his stepmother who enquired why the appellant had returned so early. P.W.2 asked him if he wanted a bath to which he replied affirmatively. While P.W.2 requested her daughter to fetch water for the appellant, the latter fetched water by himself and had his bath. Shortly thereafter, P.W.2 heard a shout from the deceased who was sleeping inside the house, on getting into the house she found the deceased in a pool of blood and the appellant hiding behind the door with a matchet (exhibit C) in his hand. On seeing the P.W.2, the appellant jumped through the window and escaped to a neighbouring village from where he was subsequently arrested after narrating to the villagers what he had done. Meanwhile, the deceased who was being rushed to the hospital died on the way. In his statement to the police, (exhibit B) made on 5/2/87, the very day of the incident, the appellant gave a coherent and rational account of the incident confessing that he killed the deceased. He said: "This morning my father Sunday Guobadia say make me and my brother, Victor