A teenager was arrested Sunday on suspicion of killing a high school friend who was visiting her apartment in Sasebo, Nagasaki Prefecture, police said.

The 15-year-old girl, whose name was withheld as she is a minor, allegedly used a blunt instrument to kill Aiwa Matsuo, also 15, around 8 p.m. Saturday by attacking her from behind with over a dozen blows to the head and strangling her. Her head and left hand had been chopped off as well, they said.

The suspect was arrested after confessing, they said.