A woman has told German investigators she was held captive for around three months and was physically abused by a couple who are in custody over the deaths of two other women.

Investigators travelled to the Berlin area to hear the woman's account of her dealings with the couple - a man and his ex-wife who still lived together.

Authorities believe that the couple, from a village near the western town of Hoexter, held another woman for nearly two months and abused her so badly that she died in April.

They have also said they believe the couple killed and dismembered a victim in 2014.

The 51-year-old woman in the Berlin area, who was not identified, said she answered a personal ad placed by the husband in August 2011 and travelled to their house, police in western Germany said. She was not attacked during that three-week visit and stayed in touch with the man.

The woman returned to the couple's home at the end of 2011. She said she was locked inside the house with "no possibility of fleeing" and was physically abused by both suspects, according to police.

In March 2012, they said, she was taken to a station and put on a train home following a "significant physical dispute". She did not contact police at the time because of threats of further violence.

The woman contacted police on Friday after seeing pictures of the house in German media.

The suspects have been under investigation since April 21, when they called an ambulance after their car broke down and rescuers found a woman inside suffering from head injuries and other abuse. She died shortly afterwards in hospital and doctors alerted authorities to the signs of abuse.

Prosecutors said their motive is still unclear but it appeared to be more about power and control than sexual reasons.