Police in Tokyo have arrested a 31-year-old daughter of the couple whose burnt bodies were found in a mountain area in Tochigi Prefecture, north of Tokyo, this April. She is the 7th person arrested in the double-murder case.

The victims, Takarajima Ryutaro, and his wife, Sachiko, ran a company that operated many restaurants in Tokyo's Ueno district.

On Thursday, the police arrested their daughter, Manami, for her suspected role in the murder case.

Since the bodies were found in woods in the town of Nasu in April, six men have been arrested and indicted on charges of damaging and abandoning the bodies. The six were also arrested again on suspicion of murder.

The police believe Sekine Seiha, the 32-year-old common-law husband of the victims' daughter, is the mastermind.

The police say that an analysis of smartphone records has led them to believe that Manami herself was also involved in the murder case.

She had served as an executive of the company run by her parents, but she left the post in January this year.

Her common-law husband, Sekine, also worked as a manager at the company. He reportedly had major differences with Takarajima and his wife over business policies regarding marketing and allocation of employees.

The police suspect that the internal conflict in business may have led to the murders.