The Metropolitan Police Department rearrested Kenichi Hosoya, 43, and his wife Shiho Hosoya, 38, both former company executives who ran a ryokan (Japanese inn) in Tokyo's Asakusa district, on Friday on suspicion of murdering his father in 2018, following their arrests for allegedly killing his sister and 4-year-old daughter.

Although both suspects have invoked their right to remain silent, investigators are looking at inheritance as the primary motive.

The couple have been detained since February on suspicion of administering psychotropic drugs and ethylene glycol, an antifreeze substance used in car engines, to their daughter Yoshiki, resulting in her death in March 2023. They were rearrested on suspicion of murdering Minako Hosoya, 41, by making her ingest ethylene glycol around April 2018.