A teenager arrested after stabbing a teacher at a junior high school near Tokyo told police he desired to see "what would happen when someone is killed," investigative sources said Thursday.

The 17-year-old also said he chose to enter the Misasa Junior High School around noon as classes would be in session at that time, according to the sources. He had at least three knives in his possession during the incident in Toda, Saitama Prefecture.

Members of staff and others watch on as students at Misasa Junior High School come to school on the first day after an intruder attacked a teacher in Toda, Saitama Prefecture, on March 2, 2023. (Kyodo)

The teenager, a high school student from the neighboring city of Saitama, did not know the teacher he had attacked. His name is being withheld because he is a minor.

According to Saitama Prefectural Police, the alleged assailant attempted to enter a classroom on the third floor of Misasa Junior High School through its back door at around 12:20 p.m. on Wednesday while first-year students were taking an end-of-semester test.

A 60-year-old teacher acting as the exam proctor got into a scuffle with the student and suffered multiple injuries to his arms and lower torso, including a deep stab wound in his abdomen.

The 28 students in the classroom at the time safely evacuated. The suspect was restrained by teachers who rushed to the scene, and he was arrested on suspicion of attempted murder.

Police later found at least one knife, which they believe to be the suspect's, from a school corridor, as well as a smartphone and a knife from his home.

According to investigative sources, the teenager went to the school by bicycle. The school's main entrance was not locked, and security camera footage showed a person who appeared to be the teen entering the compound.

"I was interested in killing anyone," the suspect was quoted as saying. "I also wanted to see what would happen when someone is killed."

The police are also looking into the teenager's possible involvement in a recent spate of dead, mutilated cats found in the city of Saitama after he implied he was behind the incidents, the sources said.

The cases came to light in mid-February when cat parts were found on a park bench and hanging from a climbing frame at an elementary school.

The body of a beheaded cat was also discovered partly buried in a field in the city of Saitama on Sunday. What appeared to be the upper part of one was also found later that day on a road about 300 meters from the field.

Speaking at a regular press conference on Thursday, Chief Cabinet Secretary Hirokazu Matsuno said while the government has implemented seminars and other initiatives to prepare school staff for such events, it will examine what happened at the school in Toda and take necessary safety measures.

Schools in Japan have improved safety measures since a 2001 incident in which a knife-wielding man entered an elementary school in Ikeda, Osaka Prefecture, and killed eight students, wounding 15 others.

But while most schools have crisis management manuals in place, challenges remain around the introduction of costly measures, such as installing security cameras and hiring security guards.

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Knife-wielding teen attacks teacher in school near Tokyo, arrested