A Chicago man confessed to killing his girlfriend's mother, whose body was found last month in a suitcase outside a hotel in Indonesia, police in Bali tell CNN.

The girlfriend also confessed to being involved and trying to get rid of her mother's body, police say.

Heather Mack, 19, and Tommy Schaefer, 21, have been detained as suspects in the murder in the death of Mack's mother, Sheila von Weise Mack, and "it appears that the motive for the killing was because she was against Schaefer's relationship with Heather," Bali police spokesman Hery Wiyanto told CNN.

Formal charges are pending, as the investigation continues.

What exactly happened in room 317 of the St. Regis Bali Resort and the exact role Heather Mack has is still under investigation, said Denpasar police Chief Djoko Hari Utomo.

Evidence includes surveillance video of an argument between the couple and the victim at the hotel and of the two suspects entering and exiting the hotel room, according to Wiyanto.

The badly beaten body of Sheila Mack, 61, was wrapped in a blood-stained bed sheet and placed in a large hard-sided suitcase, Indonesian authorities said.

The young couple allegedly put the suitcase in the trunk of a taxi outside the hotel on August 12 and went back into the hotel, telling the cab driver that they would be back, authorities said.

After a lengthy wait, the cab driver noticed blood and contacted police. Authorities at the South Kuta station in Bali opened the case and found the body, police said.

The daughter and her boyfriend were later found at another hotel about 15 kilometers (9 miles) from the St. Regis. The couple's St. Regis room was "very messy," with clothes still inside, authorities said.

The couple initially told police they had been taken captive at the resort by an armed gang, whose members killed Sheila Mack, but they escaped, CNN affiliate Trans TV reported.

(CNN)