A 15-year-old junior high school student who has been arrested in connection with the fatal stabbing of an 84-year-old woman has told investigators he "just wanted to kill someone," authorities said Tuesday.

The suspect, from the city of Chiba, has admitted to the killing, telling investigators “I didn’t care who it was,” in what police believe was an indiscriminate attack. The teen was turned over to prosecutors the same day.

The incident occurred shortly after 5 p.m. on Sunday in the city’s Wakaba Ward. A passerby discovered the victim, Yayoi Takahashi, lying on the street with stab wounds to her back, lying in a pool of blood, and immediately called emergency services. Police were unable to find the murder weapon at the scene.

Takahashi was pronounced dead at a hospital shortly after. She lived nearby and had no known connection to the suspect.

Surveillance footage showed the teen walking toward the scene of the crime at 5:03 p.m. and moving away at 5:07 p.m., though the stabbing itself was not captured.

On Monday, the boy was taken into custody and formally arrested on suspicion of murder later in the day. Investigators searched the suspect’s residence and recovered a knife believed to have been used in the attack.

Family members of the suspect responded to media questions on Monday.

“There was nothing unusual about his behavior that evening. He didn’t seem restless or anything,” the teen’s father told broadcaster TBS.

According to his family, the boy has had behavioral problems, such as running away from home and being taken to the police station roughly once a month.

“The police used to tell him, ‘If you do something again, you’ll get arrested.’ I thought that might serve as a deterrent and kept reporting things, but none of it led to anything,” said the father.

The boy's grandfather said, “If he didn’t care who it was, then he should have killed me.

“There's no way to make sense of it, no way to apologize.”