HONG KONG (AP) — A foreign man living in Hong Kong has been arrested on suspicion of killing a Southeast Asian woman at a waterfall inside a park on the Chinese territory.

The woman, who was about 25 years old, was a domestic worker in Hong Kong but did not work for the suspect, Police Commissioner Sin Kwok-ming told reporters late Tuesday.

The woman went to the waterfall inside a park in Pok Fu Lam on Hong Kong Island on Sunday night with the suspect, but he left alone in a taxi after staying there for about half an hour, police said.

On Monday morning, residents saw the woman’s body floating in the pond below the waterfall, Sin said.

An initial autopsy showed the woman drowned after being hit in the head with an unspecified hard object. Sin said the woman had injuries to her head and limbs.

The suspect and his wife, a Hong Kong woman, left for mainland China before officers arrested them when they returned to the city on Tuesday, Sin said. The man was detained on suspicion of murder and his wife was detained for assisting criminals.

The man holds a Hong Kong ID card, but police did not say which country he or the victim was from.

“We found so many unreasonable things related to the arrested man. He did not report to the police and immediately left Hong Kong after the incident. Some evidence related to him also disappeared,” Sin said.

The investigation continues. The man and his wife were still in custody and had not been charged as of Wednesday morning, police said.

“This case involves a person’s life and we take that very seriously. We will carefully unravel every detail to uncover the truth and bring justice to the deceased,” said Sin.