Lau Wing-wah was being treated for the wrong condition when he lost control and killed his mother, the court heard. Dr Singer said doctors had been 'experimenting' with the drug lithium to see if he responded to it.

But the drug is used to treat a disorder from which Lau was not suffering. Dr Singer said it caused Lau to suffer side effects which led him to stop taking his medication altogether.

It was in these circumstances that he snapped after being scolded by his mother, and used a chopper to cut off her head.