A 56-year-old man who was arrested after knives were left on Prince Hisahito's school desk in Tokyo has told investigators he intended to stab the 12-year-old heir to the throne, investigative sources said Wednesday.

Kaoru Hasegawa admitted to leaving the knives and criticized Japan's imperial system after he was 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.

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

On April 26, 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 after.

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 the police.

The incident occurred as Japan awaited the abdication of former Emperor 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 Fumihito, 53, the younger brother of the 59-year-old emperor.

In the wake of the incident, the education ministry has instructed education boards overseeing elementary schools, junior high schools and high schools nationwide to enhance security measures.

The notice dated Tuesday reminds them to set up multiple check points at school gates and entrances to look out for suspicious individuals, among other steps.

(Prince Hisahito (C), is pictured with his parents before attending the entrance ceremony for a junior high school in Tokyo, on April 8, 2019.)