Use of basic verbs, katakana revision, school subjects, school words, and use of kara as a sentence ending particle.
There is no clear outcome for who the culprit is. The idea is to use critical thinking and kara as a particle in this instance.
Then the students can reverse engineer the sheet to create their own mystery task.
Top range class should finish it in 1-2 lessons, may take longer for classes of mixed abilities.