'Youth compounds it, but can youth be the only reason? When emotions take over the rational self, anyone can do silly, irrational things. Anyone can be influenced if the right buttons are pushed.'
More often than not, the button pushed is love.
Muhammad Nasir Abdul Aziz, 17, killed his older lover's husband as she threatened to marry someone else willing to do so. She also told him she was 'suffering' with her husband.
Dr Tan, who saw her before he entered private practice, was of the opinion she 'influenced', rather than 'manipulated' the boy: 'She had a moderate depressive episode. She's young, not very bright and seemed trapped in her marriage. She didn't know how to get out - the only way she knew was to influence a young boy who was blinded with love.'
But love could push even mature adults to kill, he said, pointing to a 1999 murder. Then, Julaiha Begum, 52, convinced her younger lover, Loganatha Venkatesan, 25, and another man to kill her husband. All three were hanged in 2001.
Other psychiatrists pointed out cases where mothers let their boyfriends sleep with their daughters.
Dr Tan said: 'Adults have done it. It's not necessarily youth that causes people to do things. For love, a lot of people can do a lot of things.'