She looked into the wishing well. It was full of pennies that people had thrown in. She could either throw a penny in herself, and make a wish, or she could throw in the knife. She had carefully wiped off all the fingerprints and had even boiled it in caustic soda: surely now there would be no trace of anything, and her wish to avoid retribution would come true.
Her arm curved as she threw, and the knife flew upwards and then clattered as it landed at the bottom of the well. Then she heard a little girl’s voice behind her. “Mummy, I saw that lady throw something into the well. I’m going to ask my fairy to grant her wish.”
The fairy stories all say that fairies grant wishes; none of them say that they protect witnesses.