Two charred bodies, with their faces bound with adhesive tape, were discovered Tuesday on a riverbed in the town of Nasu, Tochigi Prefecture, police said.
Police are questioning a man in his 20s on a voluntary basis in relation to the incident, under the belief that multiple people might have been involved, NHK reported.
Police discovered the bodies as they rushed to the site following a report from a local man at approximately 8:10 a.m. Tuesday. The man initially thought that mannequins were being burned.
Police are investigating the incident, believing that the two are likely to have been killed.
According to police sources, one of the bodies has been identified as 55-year-old Ryutaro Takarajima, whose address and occupation are currently unknown.
The alert was first raised earlier the same day, at around 6:50 a.m., by another local resident who saw flames on the riverbed and contacted an acquaintance, who verified the situation before reporting it to the police.
Investigative sources said the bodies were burned all over, with their heads each covered with a plastic bag and adhesive tape bound over them. Their hands and legs were tied with zip ties.
A portable can that smelled like gasoline was found nearby and the police believe someone might have poured oil over the pair and set it alight.
The police have scheduled autopsies for the bodies to ascertain the precise cause of death.
The incident site is located around 17 kilometers east of Nasushiobara Station, in an area characterized by mountainous terrain and scattered housing.