The 16-year-old boy arrested in the fatal stabbing of his schoolmate, Yua Koyama, 15, said he locked the door to her house with a key he found inside a bag he had stolen from the girl earlier, investigative sources said Monday.
Koyama's bag, which was stolen Nov. 2, was found near where an elementary school used to stand.
Her wallet was not found and police initially thought the theft was unrelated to the murder, which occurred on the evening of Nov. 10.
According to investigators, the boy told police he stole Koyama's bag as a prank. He also said he used the key to lock Koyama's apartment after killing her.
Investigators alleged the boy broke into the apartment on his way home from school, took a knife from the kitchen and stabbed Koyama to death.
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