A 51-year-old man in Nishi-asai, Shiga Prefecture, was arrested Wednesday on suspicion of strangling his 19-year-old son, police said.
The suspect was identified as Susumu Nakagoshi.
According to investigators, he strangled his son, Tetsuya, with a rope at around 7 a.m. as the vocational school student was asleep in his room. He then called police to inform them of the crime.
When investigators arrived, they found the deceased lying on his bed covered with a futon. The father was in the room. There were no signs of struggle, police said.
Nakagoshi was quoted as telling police he was afraid his son, who had fallen in with a bad crowd, would at some point cause trouble for his family and others.
Nakagoshi lives with his parents, his wife and two children. Police said they would question other family members to further pinpoint a motive.