Prosecutors have decided to conduct a psychiatric test on the 17-year-old boy arrested on suspicion of killing his mother and severing her head and right arm in Fukushima Prefecture, investigative sources have said.

The Fukushima District Public Prosecutor's Office is planning to have the high school student from Aizuwakamatsu undergo a comprehensive test, possibly next week, so psychiatrists can fully assess his mental state, the sources said Wednesday. The assessment is likely to take from weeks to months.

The prosecutors will try to determine whether the student, whose name is being withheld as he is a minor, is mentally competent by interviewing him and looking into his upbringing, they said.