Two knives were found near the desk of Prince Hisahito, the 12-year-old grandson of Emperor Akihito, at his junior high school, with security camera footage showing a man wanted in connection with the incident trespassing on school grounds, police said Saturday.

The footage shows a helmeted middle-aged man dressed in blue entering Ochanomizu University Junior High School on Friday around noon, according to the police.

Prince Hisahito, who began classes this month, was not in the classroom, which was empty at the time when the knives are believed to have been left there.

The Metropolitan Police Department is searching for the man, who is suspected of disguising himself as a construction worker to get in to leave the knives — thought to be fruit knives.

The incident came just ahead of next week’s Imperial succession, which will make the young prince second in line to the Chrysanthemum Throne. Prince Akishino, father of Prince Hisahito, will be first in the line after the succession.

There was a seating chart in the classroom and the Metropolitan Police Department suspects that someone who saw it identified where the prince sits, according to investigative sources.

The hilts of the knives were attached by adhesive tape to a stick, the sources said, and the combination was placed across the prince’s desk and the one next to it.

The blades of the knives were painted pink, they added.

Whenever Prince Hisahito leaves his residence, he is guarded by police officers but at school they stand by on campus and do not accompany him inside buildings or his classrooms, according to an Imperial Household Agency official.

Students of the women’s university, which is on the same campus, were surprised that the incident occurred despite tight security.

Guards at the premise’s two main gates have always checked the identities of visitors and asked students to show their cards, according to a student attending its graduate school.

“I have never worried about safety. I can’t believe such an incident happened,” said the 23-year-old student.

“It is difficult for an outsider to freely enter the campus,” a senior student at the university also said.