Police on Wednesday arrested a 42-year-old man in connection with the deaths of his parents, who were found fatally stabbed the day before in a factory the family ran in Takarazuka, Hyogo Prefecture.
The suspect's name was not immediately available, and he was not responding to the charges, the police said.
Shiro Shinagawa, 67, and his wife, 65, whose name was not released, were found dead with stab wounds on the residential floor of their small factory, which manufactures food-processing machines, the police said.
An employee called the police after the bodies were discovered at around 4:30 p.m. Tuesday.
Their son lives there as well. There were no signs of theft and the weapon used in the slayings had not been found, the police said.
The son was spotted hours later driving in southern Kyoto Prefecture and police started interviewing him over the deaths, they said.
A factory employee was quoted as telling investigators he had been unable to locate the couple since around Monday.
A neighbor said he had heard no voices at the time the slayings were believed to have occurred, and that he could not believe the killings had taken place in such a serene residential area.