It's by Roald Dahl, a Norwegian author. Well, Norwegian-British (norwegian parents, summerhouse in Norway, but grew up in England), but we like to think of him as just ours. He's amazing, and has written both horror stories and children's books (Charlie and the chocolate faktory, anyone?)
I'm laughing because I was in a group at my school with the principle and we read advanced novels and he made us read this and later he told us it was one of his favourite stories and i was really concerned because murder and all that but yeah good book
"the evidence could be right here under our noses" Mary giggled
You can find them all on YouTube!