A 15-year-old male was arrested Thursday for an alleged bomb threat targeting a high school in Bizen, Okayama Prefecture, that was evacuated earlier this week, police said.

The teen is suspected of leaving a handwritten note that said: "A bomb has been planted at school" in a shoe locker at Bizen Ryokuyo High School on Tuesday.

The prefectural school alerted the police after finding the memo in the morning. The roughly 460 students were all evacuated and sent home.

On Thursday morning, a letter encouraging police to do their best to catch the sender was found at the school in the same style of writing used in Monday's note, the police said.

The police said they questioned school officials and tracked down the teen, who admitted to the allegations. They said they are investigating the case as a prank.

The teen was only identified as a first-year student from the city because it has not been clarified whether he actually attends the school in question, and is a minor.