DENPASAR (AFP) - Indonesian police have completed their probe into an American man and his girlfriend accused of killing the woman's mother in Bali and stuffing her body in a suitcase, a prosecutor said Monday, adding the pair was expected to go on trial next month.

He also said 19-year-old Heather Mack, who is pregnant, and her boyfriend Tommy Schaefer were being transferred from police cells to the resort island's notorious Kerobokan jail, where prisoners live in cramped, filthy conditions and drug abuse is widespread.

The battered body of Sheila von Wiese Mack, 62, was found in a suitcase in the boot of a taxi in front of an exclusive hotel in the upscale Nusa Dua resort area in August.

Mack and Schaefer, 21, had been staying with her but fled to another part of the island after the killing. They were caught the following day and police have said they could face the death penalty if found guilty of premeditated murder.

Prosecutor Eddy Artha Wijaya told reporters in the Balinese capital Denpasar that police had finished their investigation and handed responsibility to the prosecution service.

"We have received the case file from the police," he said. Prosecutors have an initial 20 days to draw up charges and Wijaya said he hoped the pair would face trial in January.

If the case does proceed to court, Mack and Schaefer will be formally charged at their first appearance, which is the usual procedure in the Indonesian legal system.

They had been in police holding cells during the police investigation. But now that probe had wrapped up they would be moved later Monday to Kerobokan, Wijaya said.

Mack's lawyer, Raja Nasution, insisted that "she will be more comfortable there as it's bigger". He added that she would go to hospital every month to check on the progress of her pregnancy.

The victim and the suspects are all from the Chicago area.