Sesuatu perbuatan yang dilakukan oleh orang yang tidak sempurna akal bukan merupakan satu kesalahan. Ini boleh dilihat dengan jelas di dalam SEKSYEN 84 KANUN KESEKSAAN yang menyatakan seperti berikut:-
84. Perbuatan seseorang yang tidak sempurna akal.
Isu ini juga telah dijelaskan di dalam kes PENDAKWA RAYA V ZAINAL ABIDIN BIN MAT ZAID  1 CLJ 147:-
“When the defence of insanity is raised the court thus needs to consider two matters, namely: (i) 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 (ii) 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 incapable of knowing the nature of his act as being wrong or against the law. It is also settled law that the burden of proof rests on the person who raises the defence of insanity.”