A forensic expert has cast doubt on drowning as the cause of death for Hong Kong Design Institute student Chan Yin-lam.

Philip Beh Swan-lip, the principal clinical practitioner at the University of Hong Kong's medical school, testified as an expert witness before coroner Ko Wai-hung and a five-strong jury yesterday.

In a report by Beh, at the request of the coroner's court, he said that Chan's autopsy result was unusual for a death caused by drowning.

"People who were normally drowned will have both their lungs filled with the same amount of water, as well as in the stomach, but Chan's results showed that only the left lung matches such a description for drowning," he said.

The jury asked whether the amount of water would be different if the person was placed in the water consciously, unconsciously or after death. Beh said that in an "after-death" instance, the lungs would be filled with less water but equal in each lung.

Beh said he could only determine Chan's body was submerged in water.

He also said that in a drowning case, diatoms of the nearby water would be found in the body.

A diatom test is used to determine if a person drowned, but such a test was not done on the body, he said.

Beh also disputed government pathologist Li Yuk-wah's claim that there are no diatoms in local waters. He said the test is uncommon in Hong Kong, partly since there is no relevant database.

Beh also raised concerns over why the body was naked, pointing out that loose clothing could wash away but underwear would be harder to detach.

However, Beh did not know whether Chan was wearing any clothing at the time. In addition, he also noted that sexual abuse DNA evidence from Chan's vagina could be diluted as Chan's body was soaked in the water.

The inquest continues today.

Chan Yin-lam and her mother.

Philip Beh

Expert report casts doubt over teen drowning verdict