Heather Mack, 19, and her boyfriend Tommy Schaefer, 21, both from Chicago, were arrested Wednesday in Bali's Kuta area, a day after the body of Sheila von Wiese-Mack was found inside the trunk of a taxi parked in front of the St Regis Bali Resort.
The charges are based on witnesses and crime scene evidence, said Bali deputy police chief Brig Gen Gusti Ngurah Raharja Subyakta. He added that the couple refused to speak to investigators without a lawyer following initial questioning, and were being tested for illegal drugs.
However, after two hours, Mack and Schaefer had not reappeared. Hotel security guards who found blood spots on the suitcase suggested the driver take the taxi to the police station, where officers opened the suitcase and discovered the body.
Von Wiese-Mack, also from Chicago, and her daughter arrived at the St Regis on Saturday, while Schaefer checked in on Monday, police said.
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CCTV footage shows that the victim had an argument with Schaefer on Monday in the hotel's lobby.
"We found scars on both forearms and the broken left-hand fingernail," Alit said following an external examination.
"That indicated a resistance in a fight."
During initial questioning Wednesday, Mack acknowledged her mother died, but refused to disclose how, according to Haposan Sihombing, an Indonesian lawyer assigned by police to accompany the couple.
Sihombing said Mack and her mother arrived in Bali on Aug 4, and stayed first at Simanyak Hotel before moving to St Regis on Aug 9.
Authorities in an upscale Chicago suburb, meanwhile, examined records of 86 incidents in which police were called to the family's house in Oak Park where von Wiese-Mack lived with her daughter.
Von Wiese-Mack was the widow of highly regarded jazz and classical composer James L Mack of Oak Park, Illinois, who died in 2006 at age 76.