MISAWA, Japan — Police in northern Japan have launched an investigation into the death of a Misawa woman found dead in the trunk of a burning car last week in Hachinohe, a city about 15 miles south of here.

Naomi Kimura, 33, owned a bar in downtown Misawa frequented by foreigners. An Aomori prefectural police spokesman in Misawa would not release the name of the bar, which is located on the city’s main street and a five-minute walk from Misawa Air Base.

Local media reports have said acquaintances of the woman, including some Americans, are being questioned as part of the investigation. But the police spokesman declined to comment on whether any base workers or other Americans, including the woman’s ex-husband, were questioned. No one has been arrested yet, the spokesman said Tuesday, adding that questioning so far has been voluntary.

A Japan Railways employee reported finding a burning vehicle Friday, just after midnight, on a stretch of railroad about 100 feet from a track crossing in the Samemachi district of Hachinohe. Japanese police and firefighters discovered Kimura’s burned body in the trunk. The car reportedly belonged to her.

Misawa and Hachinohe police are conducting the investigation. The Misawa police spokesman said the cause of the women’s death has not been determined.

According to local news reports, Kimura was last seen around 2:30 a.m. Thursday, when she allegedly left her bar with an American male in his 20s and a female bar employee.

Misawa base officials declined to comment on whether anyone assigned to the base was being questioned, since the investigation is being handled by Japanese police.

Chiyomi Sumida and Hana Kusumoto contributed to this story.