DENPASAR (REUTERS) - Indonesian police on Thursday ran psychiatric tests on the teenage daughter of an American woman found dead inside a suitcase on the resort island of Bali.

Police arrested the daughter, Heather Mack, 19, and her boyfriend, Tommy Schaefer, 21, on Wednesday after a taxi driver found a battered body in a suitcase outside the St. Regis luxury hotel in Nusa Dua, Bali.

The body was identified by hospital officials as Chicago-based Sheila von Wiese-Mack, 62.

Neither Mack nor Schaefer has been charged but police have detained them as suspects. "We have done blood and psychiatric tests to try to find out their motive in the case, maybe they are mentally unstable," Mr Djoko Hariutomo, police chief for Bali's provincial capital Denpasar, told reporters. "So far we haven't gotten any information on what is behind the murder. Is it financial or something else? We don't know."

Television broadcast images of Mack, dressed in a pale grey hoodie and denim shorts, laughing and telling a group of reporters following her, "You are crazy," as she walked between rooms in the police station.

Police said the young couple on Tuesday left a bloodied suitcase and other luggage in the taxi, and went to check out of the five-star hotel, where a single room can cost as much as US$1,340 (S$1,675.40) a night.

The couple did not return, so the taxi driver checked the luggage and found the body. An official at the hospital that conducted the autopsy said Ms von Wiese-Mack had been repeatedly hit on the face and head with a blunt object.

A St. Regis hotel official said the incident was believed to have taken place in a room booked by Schaefer.

Mack and Schaefer were apprehended on Wednesday at a budget hotel about 1.6 km from the St. Regis hotel after a day-long search by police.

Staff at the Risata Bali resort said they were immediately suspicious of the couple after they checked in without luggage.

Risata Bali security confirmed their identities after Schaefer asked resort staff for a voucher to use the Internet and they alerted authorities, said Mr Nyoman Wija, a hotel manager.

Police have appointed an Indonesian lawyer to represent the couple, but they have asked for US legal representation. "She doesn't want to comment on the incident and she declined to give any information," Mr Haposan Sihombing, an Indonesian lawyer appointed by police to represent Mack, told Reuters late on Wednesday. "She kept asking to be represented by a lawyer from the United States," Mr Sihombing said.

The US State Department is aware of reports of a US citizen's death in Bali and the arrests of two people in connection with the case, said State Department spokeswoman Marie Harf.

She declined to give details due to privacy considerations. "Obviously we are monitoring it and will provide any consular access as appropriate," Mr Harf said.

An official with the US consulate general in Bali, who met Mack at the police station on Thursday, declined to comment after the meeting.

The Mack family lived for a number of years in the Chicago suburb of Oak Park, Illinois.

Oak Park spokesman David Powers said on Wednesday police responded to 86 calls from the Mack home due to incidents between mother and daughter from 2004 through to June 2013.

No arrests were ever made from the calls, which were a combination of reports of domestic violence, theft, missing person and 911 hang-ups, Mr Powers said.

Von Wiese-Mack more recently had moved to a condominium in Chicago. Her husband, and Heather's father, classical music composer James Mack, died in 2006.

Laura Voigt, a pianist in Oak Park and friend of James Mack, said she remembered seeing mother and daughter fight outside the local high school one morning. "I was worried about Sheila," Voigt said.

Von Wiese-Mack had worked as an editor for famed oral historian Studs Terkel and later studied with Nobel literature laureate Saul Bellow at the University of Chicago.

Georgia Parchem, a neighbour and friend in Oak Park, said von Wiese-Mack was a "lovely, charming woman" and the Macks often held parties involving "artists and friends from all over the city".