A pregnancy for Heather Mack, 19, would complicate police calls for her to face the firing squad over a crime they now believe was premeditated, and should carry the death penalty.

Police say they have enough evidence to prove that Mack and her co-accused, boyfriend Tommy Schaeffer, 21, bludgeoned Heather’s mother, Sheila Von Wiese Mack, 62, to death before putting her body in a suitcase and then into a taxi.

Denpasar police chief Djoko Hari Utomo confirmed that Mack had made the pregnancy claim on Thursday and was taken on Friday to see an obstetrician and gynaecologist.

However, Mr Djoko said, "we have to verify every claim made by the two suspects".

He could not confirm one of many rumours doing the rounds in Bali, that Mack and Tommy Schaeffer had had sex in the room after the murder took place.

"We don't know what happened in the room or what they did in there before or after the murder because we are still unable to question them," Mr Djoko said.

"They also refuse to answer questions about what the fight with the victim was about."

He said police were keeping the pair in different places - Mack at the Denpasar police station and Schaeffer at Bali police station - so they could not "match up" their stories.

Police have not yet charged the pair, but revealed on Friday that they may face an Indonesian firing squad.

Mack’s American lawyer, Michael Elkin, however, says his client is innocent.

Any allegation that she was involved in her mother's death were not true and "will be disproven as the investigation continues or at the conclusion of trial, if formal charges are indeed filed," TV station CBS Chicago reported.

Mr Elkin has been hired by Mack to find her a lawyer in Bali, and CBS has reported that the US Consulate had arranged for him to speak to his client on Thursday.

The couple underwent physical testing in hospital on Friday as Bali police chief Benny Mokalu said the charges might be upgraded because, “I am leaning more towards thinking the murder was premeditated”.

Until now, police have contemplated a lesser charge with a 15 year maximum jail sentence.

“Why premeditated? Because the victim was stuffed into a bag. It shows planning,” Mr Benny said.

The couple have still not been questioned because they are waiting for a lawyer. But Mr Benny said: “Even without confessions or a statement, based on the evidence collected - which includes CCTV footage, fingerprints, the items used, the bag - it all points to them as the perpetrators.”

He said both would undergo psychological testing for “supporting evidence,” but he added: “there's no psychological aspect; it's pure premeditated murder”.

Police allege the pair bludgeoned Von-Wiese Mack, 62, with a heavy glass object before putting the body in a grey suitcase, wrapping that in a hotel bed sheet and loading it into a pre-ordered taxi.

They say Mrs Mack was  killed on Tuesday morning, after which police say the pair mopped up the blood with towels and sheets, hid the evidence, then fled the hotel for the airport.

They were arrested on Wednesday morning sleeping at a hotel after having unsuccessfully tried to obtain new passports at the airport.

With Amilia Rosa