Tokyo police are investigating how two knives ended up beside the school desk of Prince Hisahito, the grandson of Emperor Akihito.
Investigators said the knives were found on Friday at Ochanomizu University Junior High School in Tokyo's Bunkyo Ward which the prince attends. They said there was no one in the classroom at the time as the students were in another part of the school.
The Tokyo Metropolitan Police Department said surveillance cameras captured images of a middle-aged man dressed in a blue top and bottom and wearing a helmet who entered the building . He reportedly entered posing as a construction worker.
Police are investigating whether there is any connection between the trespasser and the knives.
Prince Hisahito is the son of Prince Akishino and Princess Kiko. He began his studies at the junior high school earlier this month.