Police arrested five individuals including four teenagers on Tuesday, after the body of a 17-year-old boy with Chinese nationality, Ukawa Saito, was found in a central Japan lake earlier this month.

The five are Neo Horiuchi, 21, from Hamamatsu, Shizuoka Prefecture, an 18-year-old man with Philippine nationality and three 17-year-old boys, including one with Brazilian nationality. They were arrested on charges including assaulting Saito, who was enrolled at a correspondence high school.

The police are investigating the relationship between the five and Saito.

Horiuchi allegedly conspired with the four boys to beat and injure Saito and confine him in a car in Hamamatsu in the early morning of Feb. 5.

Saito's body was found by a man fishing in the lake in the city of Kosai on Feb. 9, according to Shizuoka police. A forensic autopsy revealed that the cause of death was drowning, while the body had multiple internal hemorrhages.

Saito left his home in Fukuroi, a city in western Shizuoka Prefecture, at around 7 p.m. on Feb. 4, telling his family that he was going out to play. Three days later, his family submitted a search request.

It has been confirmed that Saito was at an acquaintance's house in Hamamatsu in the early hours of Feb. 5, but he later disappeared.

The suspects were with Saito at the Hamamatsu house, police sources said.