A 56-year-old man who was arrested over leaving knives on Prince Hisahito’s classroom desk at a Tokyo school has told investigators he had intended to stab the 12-year-old, investigative sources said Wednesday.

Kaoru Hasegawa admitted to leaving the knives and criticized Japan’s imperial system after being apprehended on April 29 for allegedly trespassing on the grounds of Ochanomizu University Junior High School, which is attended by the nephew of Emperor Naruhito, according to the sources.

The prince and his fellow students were outside the classroom when the two knives were left, at around 11 a.m. on April 26.

The police have not linked Hasegawa with any group, they said.

On the day of the incident, an aluminum bar with two fruit knives attached by duct tape to one end was found placed across the prince’s desk and the one next to it. The blades of the knives were painted pink but no written message was left at the scene.

Security cameras captured images of a man, believed to be Hasegawa, walking past the main gate of the university in the morning and leaving less than an hour later.

The man, wearing blue clothing with a helmet, mask and gloves, entered the junior high school after telling a staffer that he was a plumber, according to police.

The incident occurred as Japan awaited the abdication of Emperor Emeritus Akihito on April 30 and the enthronement of Emperor Naruhito on May 1.

The imperial succession promoted Prince Hisahito to second in line to the throne after his father Crown Prince Akishino, 53, the younger brother of the 59-year-old emperor.

In the wake of the incident, the education ministry has notified education boards overseeing elementary schools, junior high schools and high schools nationwide to enhance security measures. The notice, dated Tuesday, also reminds officials to set up multiple checkpoints at school gates and entrances to look out for suspicious individuals, among other steps.