A 16-year-old Japanese girl described by friends as emotionally unstable has been charged with bludgeoning and decapitating a 15-year-old friend, telling police "I did it all by myself," the Japan News reports.

The body of Aiwa Matsuo was found early yesterday in the suspect's Sasebo apartment, where she'd lived alone since April; Aiwa's left hand and head had been cut off.

Police say the unnamed suspect hit Aiwa over the head several times with a metal instrument on Saturday night, then strangled her with a cord; an autopsy revealed Aiwa died of suffocation.

The pair had been friends since middle school.

"We are not aware of any trouble between the two," says the principal of the girls' high school. But some friends and acquaintances say the suspect suffered "emotional ups and downs," according to the Japan Times.

Now, police are looking at a series of messages posted on a popular Internet forum called 2Channel Saturday night that could be linked to the killing.

"I've tried to warm (the body) as it got cold, but it doesn't warm up ... Everyone, (do you want to know) what color the brain is?" one of the messages reads. "I'll take good care of the brain and the spinal cord, putting them in a solution."

So far, police have not determined a motive and say the suspect has not shown remorse.

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