A medical expert has rejected the suggestion from two government pathologists that a 15-year-old girl found dead at sea last year drowned, pointing to their failure to determine the teen’s time of death.

Philip Beh Swan-lip, principal clinical practitioner at the University of Hong Kong’s medical school, made his remarks at the Coroner’s Court on Wednesday, a day after the autopsy findings on Chan Yin-lam were revealed.

Chan’s body was found in the waters off Tseung Kwan O on September 22, three days after she was last seen by friends and caught on security cameras. Whether Chan, a self-taught diver, committed suicide by jumping into the sea remains unclear.

Two government pathologists who carried out the autopsy said they could not pinpoint the cause of death, but believed there was a “distinct possibility” she drowned herself, given the body lacked any apparent fatal injuries, and appeared to have been in the water for a substantial period.

But Beh challenged the accuracy of that finding, and said there were no signs Chan suffocated in the water based on the report, adding he was troubled by the fact the body was unclothed when it was discovered.

Beh, who was invited by the court to comment on the pathologists’ findings, said while loose clothing might be washed away by water currents, tight-fitting underwear was unlikely to come off naturally.

“It’s a female body, stark naked,” he said. “It’s very unsettling. This point alone is already very questionable.”

However, Beh agreed that an autopsy could not determine why the body lacked clothing.

On Tuesday, the inquest heard that the body had remained relatively intact, despite a moderate level of decomposition, suggesting Chan had not been subject to violence or sexual assault before her death.

The HKU expert agreed it was difficult to determine how the teen died in light of the body’s decomposed state, but said it was possible to locate signs of drowning based on the condition of the lungs, nose and mouth.

Some typical findings in drowning included white froth bubbling out of the nose and mouth, water inside the lungs, and swollen air sacs, the expert said, but these symptoms were absent in Chan’s body.

While pathologists found some watery fluid in both sides of the lungs and the stomach, Beh said the amount fell short of what would be found inside the body of a drowned person. He also found it strange that most of the fluid was found on only one side of the lungs.

“The difficulty is in the fact that the difference [between the amounts of fluid found in both sides of the lungs] was so huge,” he said. “The water entering the body would have gone to both lungs. It wouldn’t go sideways.”

Another way to determine the circumstances of Chan’s death, Beh said, was to conduct a diatom test – the analysis of microalgae found inside the body of the deceased.

According to Beh, it is possible to determine whether a person died before or after entering the water by checking the presence of the microorganism, which is commonly found in the environment, inside the kidneys and bone marrow.

However, such an examination had not been carried out in Chan’s case because the city’s forensic department deemed the method impractical. Beh noted that nobody in the city had done that before, and that “Hong Kong lacks the experience” to carry out the test.

The lack of a database showing the distribution of microalgae across the city also made it impossible for scientists to estimate the location where Chan entered the water, Beh added.

The last witness of the 11-day inquest, an independent psychiatrist, is expected to testify on Thursday.