Photo/Illutration The apartment building where a high school boy and the mother of a teenage girl who was a former classmate of his were discovered unconscious with assorted injuries in Takatsuki, Osaka Prefecture, on the evening of Feb. 14. (Satoru Ogawa)

TAKATSUKI, Osaka Prefecture--A 17-year-old high school student found unconscious after he broke into the apartment of a former classmate here on Valentine’s Day died of apparent self-inflicted knife injuries on Feb. 19, police said.

The student had stab wounds to his chest when he was discovered slumped in a hallway of the second floor of the apartment building on the evening of Feb. 14.

The mother of the female classmate was also found unconscious in the hallway with injuries to the back of her head.

The youth’s death came as police investigators were searching his home on suspicion of attempted murder.

A bloodstained knife was found inside the apartment. A syringe, handcuffs and a police button were also discovered at the scene, according to investigative sources.

Police believe the attack was premeditated and that the youth stabbed himself after bashing the 40-year-old woman with the baton, the sources said.

The woman lived with her teenage daughter.

The girl told investigators she was at home when a stranger disguised as a delivery man broke in.

She managed to flee from the apartment and got neighbors to alert the police while the youth and her mother scuffled inside, the sources said.

The daughter realized she “knew” the perpetrator after police informed her that he was a classmate from her junior high school.

The girl also told police she “dated him for some time” but not had any trouble with him in the two years or so after they broke up and lost contact, according to the sources.

The youth’s bicycle was discovered near the apartment.

At the time of the break-in, the youth wore a polo shirt as well as a face mask, apparently to disguise himself as a delivery worker, and carried a cardboard box.

The daughter said she did not recognize him when he broke in, the sources added.