Cheong Teik Keon v Public Prosecutor [2018] 5 MLJ 29

Cheong Teik Keon v Public Prosecutor [2018] 5 MLJ 29

Court of Appeal (Putrajaya)

Defence of Unsound Mind


1.    This is an appeal case against the decision of the trial court for the conviction for murder and death sentence.

2.    The Appellant was charged for murder under Section 302 of Penal Code for stabbing his girlfriend (‘Amanda’) to death on Valentine’s Day in the bathroom of her house.

3.    Amanda’s scream had alerted her maid and her mother which they later rushed to the scene only to witness the Appellant was standing beside Amanda’s bloody body while stabbing himself in stomach.

4.    Amanda’s brother-in-law who lived next door also a witness to the incident and saw everything.

5.    In the Appellant’s defence, he called two psychiatrists which are DW1 and DW2, who examined him more than one and a half years after the murder as his witnesses to prove that he is an unsound mind.

6.    DW1 certified that the Appellant was fit to stand trial, however DW1 opined that the Appellant was suffering major depressive disorder (MDD).

7.    DW2, on the hand stated that the Appellant was suffering from post-traumatic stress disorder (PTSD).

8.    To rebut the defence, the prosecution called in a doctor who had examined the Appellant four days after the murder and found him to be a person of sound mind.

9.    The trial judge decided to reject the defence of unsound mind on the ground that the Appellant had written an email a friend named Michelle a few hours before he killed Amanda stating that he was enraged with another man for being romantically involved with Amanda.

10.   The Appellant requested Michelle to convey his apologies to Amanda’s mom for the ‘wrong’ he was about to do.

11.    The Appellant also instructed Michelle on how she would have to deal with his assets and personal effects after his death.



1.    Whether or not the Appellant was legally insane at the time of his commission murder?


1. In deciding the issue, the Court of Appeal deliberated the pertinent considerations in particular to the mental incapacity of the Appellant to know what he did was wrong or contrary to law as required by Section 84 of the Penal Code. The provision read as follows:

“84. Nothing is an offence which is done by a person who, at the time of doing it, by reason of unsoundness of mind, is incapable of knowing the nature of the act, or that he is doing what is either wrong or contrary to law.”

2. The Court also referred to the case of Public Prosecutor v Jufri bin Nanti [2016] 1 LNS 53 in which the court in the mentioned case decided that it is not for the court to determine whether a person is legally insane, it is the psychiatrist.

3. Following that, the Court of Appeal referred to Abang Iskandar bin Abang Hashim JCA judgment in the cited case to determine whether an act could be categorised as one that has amounted to an act of insanity under Section 84 of Penal Code, which provides—

“First, there must be finding, based entirely on medical evaluation by a psychiatrist that the accused person was suffering from some kind of psychiatric condition that was affecting his cognitive faculties at the material time. That condition may qualify a person as being medically insane. But that finding per se is not sufficient to be determinate or conclusive of the fact that the accused person is legally insane, a condition with which Section 84 of the Penal Code is concerned about as a general defence under the law.

To be legally insane, as opposed to being merely medically insane, the person must be determined by the psychiatrist to have lost his cognitive faculties to a degree such that he is incapable of knowing the nature of his act, or that what he is doing is wrong or contrary to law. If the first-tier test is a medical test, then this second-tier test is a legal test.”

[Emphasis Added]

4. The Court of Appeal in this case also applied the case of Pendakwa Raya v Zainal Abidin bin Mat Zaid [1993] 1 CLJ 147 where it follows the considerations on two matters, namely-

(a) whether the accused person has successfully established, as a preliminary issue, that at the time of committing the act he was of unsound mind; and

(b) if he was of unsound mind, whether he has proven that his unsoundness of mind was of a degree to satisfy one of the tests earlier mentioned ie, that the accused was in-capable of knowing the nature of his act as being wrong or against the law.

[Emphasis Added]

5. Having correctly referred to the Penal Code and the other relevant authorities, the Court of Appeal found that it has no cause to disagree with respect to the Appellant’s counsel, the distinction drawn above makes scant difference to the overriding effect of the motive and lucidity of mind expressed just hours before the commission of the offence by the accused which negated the plea of insanity.

6. The Court of Appeal proceeded to follow the deductions made by the trial court from the email and findings as to the mental state of the Appellant where the Appellant was undoubtedly going to carry out this plan of his and he was prepared to leave this life along with the deceased.

7. From the contents of the email and given the fact that it was written some 5 hours before the incident, this was not something carried out spontaneously or on the spur of the moment.

8. The Court of Appeal does not entirely agree with the evidence of SP26 when he said that something the deceased had said that morning had so provoked him to commit the act.

9. In light of this matter, the Court also referred to the said email where the Appellant had also tendered an advanced apology to the Amanda’s mother in anticipation of what he was about to do. He further expressed that his apology was with respect to ‘the wrong I done (sic) …’. This would indicate that the accused knew that what he was about to do was wrong and therefore he felt the need to apologise to the deceased’s mother.

10. The Court also found that the use of the expression ‘wrong’ used by the accused in the email showed that he knew that what he was about to do that is, to kill the deceased, was both wrong and contrary to the law.

11. This evidence according to the Court of Appeal was sufficient to raise a reasonable doubt on the cause of the deceased’s death.

  1. The Appellant was legally sane at the time of his commission of murder.
  2. For all the above reasons, the Court of Appeal had dismissed the appeal and affirmed the conviction and death sentence passed on the Appellant.
Key Take Away
  1. The Court of Appeal, in considering the Appellant’s mental capacity under section 84 of the Penal Code, emphasized the importance of both medical and legal evaluations.
  2. Referring to the precedent cases, the Court of Appeal highlighted that a mere medical finding of psychiatric condition is not sufficient. The person must be legally determined to have lost cognitive faculties to the extent of being incapable of knowing the nature of his act.
  3. Despite the defence’s arguments, the Court of Appeal, based on the motive and lucidity expressed in an email shortly before the offence, concluded that the Appellant was not legally insane at the time of the murder, thus rejecting the plea of insanity.
  4. The Court also disagreed with certain aspects of the evidence and found the use of the term ‘wrong’ in the email indicated that the Appellant was aware of the wrongful nature of his actions, leading to the dismissal of the appeal and affirmation of his conviction and death sentence.



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