[Top: Mok Ki-yan's mother (L) being consoled by paramedics at the scene; Two-year-old Mok Ki-yan (R)]

SHE had often watched her brother-in-law play with her young daughter, so she suspected nothing when he walked into the room and picked up the little girl.

So the 28-year-old woman was completely unprepared for what happened next.

Then, he pushed open the window grille and allegedly threw her out of the window before leaping out, reported the South China Morning Post.

Two-year-old Mok Ki-yan and her uncle, interior decoration worker Mok Pak-ki, 27, were found on the pavement outside the building.

Paramedics declared them dead on the spot.

A police source said: 'Her mother ran out (of the bedroom) while her grandfather shouted for help. Five to 10 seconds later, the man also threw himself off the building. He did not say a word during the whole incident.

'Her mother and grandfather did not stop him because they were very shocked and froze on the spot. It happened all in a flash.'

The whole incident took less than 20 seconds, said the source.

Ki-yan's mum, who is from mainland China, was heard shouting repeatedly: 'My daughter was thrown down.'

She clutched the little girl in her arms and wept.

Another witness said she was still in her pyjamas, which became soaked in blood.

The tragedy, which took place on Saturday morning, came as a surprise. The family reportedly got along.

Family relations were reportedly good.

Mok had no history of mental illness, but the police suspect he might have had a hidden mental problem.

He had been suffering from insomnia, said a police source.

The girl's mother and grandmother were so distressed they had to be sent to the hospital for treatment.

Acting Superintendent Daniel Ng said officers are still investigating the murder-suicide.

Police said there had been no previous reports of domestic violence or disputes involving the family.

Psychiatry professor Lee Sing said it was possible for a person to suffer from a mental illness that his or her family did not know about.

But he added that he had not heard of a case in which a mental patient threw his or her sibling's child out of a window.

Prof Lee called for more resources to help mental patients, and said community services for mental patients were inadequate.

There have been other cases of mental patients hurting themselves or their family members.

On Thursday, an elderly man who was released from a mental hospital about six months ago leapt to his death from his flat after slashing his wife's neck with a fruit knife.

On 27 Nov, a woman is believed to have strangled teenage daughter and son before leaping to her death. She had been released from a mental hospital only two days earlier.

This article was first published in The New paper on Jan 12, 2009.