The Coroners' Court was told today that there were three possibilities which could have caused the death of six-year-old William Yau Zhen Zhong, whose body was found at a jetty in Port Klang last January.

An expert in forensic medicine at Tengku Ampuan Rahimah Hospital in Klang, Dr Nur Ayutimasery Abdullah, 38, said one of the possibilities was due to blunt trauma of the head.

The second possibility was that he could have slipped into a drain filled with water and drowned, and the third was to fall into the drain, knocked his head and died, she said during examination-in-chief by deputy public prosecutor Lee Keng Fatt.

William's body was found on Jan 24 at the jetty on Jan 24 this year, eight days after he was reported missing from Jalan Putra Mahkota, Putra Heights, Subang Jaya, after he reportedly left the family car to look for his parents who went to an electrical shop.

However, when Lee questioned whether William had drowned, Dr Nur Ayutimasery, who is the 12th witness, said that was not possible because his lung would be inflated and filled with water.

"There will also be fine bubbles at the respiratory tract which also come out from the nose and mouth, but in this case there is none because the body had become decomposed," she added.

She said there were three serious injuries found on the body, namely the skull, right rib and right shin.

"The crack on the skull could be caused by blunt force trauma," she added.

She also said that when examining William's body, she found the body having turned black.

"Based on the changes to the body, it can be concluded that William died about a week before the date of the post-mortem," she added.

The inquest before Coroner Mohd Hezri Shaharil continues on Monday.