A woman found dead in her apartment in Otowa, Aichi Prefecture, had several slash wounds to the head and abdomen, police said.
Le Thi Ly, a 24-year-old Vietnamese, was found on a futon by a friend, according to investigators. There were no signs of struggle or of the apartment having been rummaged, they said.
One of the wounds was more than 10 cm long, and the police have found no instrument that could have been used to cause it. The front door was unlocked when her body was found, the police said.
Ly arrived in Japan from Vietnam in September 2001 for vocational training and had lived in the apartment for around one year, the police said.
She worked in a car parts factory in Aichi and performed component inspection as a side job at her apartment, which was rented by a manpower company she worked for.
She was last seen by the manpower company's president at around noon Friday, preparing lunch with another woman, the police said.
The police are looking for this woman, apparently also Vietnamese, who works for the same manpower company and has since disappeared.