From the way that Mary took out her murderous weapon, the frozen gigot, to how she made the police ate it to help her wiping out the evidence.It is very obvious that Mary is very well planned, and everything was under her control.
When mary take her weapon (the ice gigot) in the fridge,to she let the gigot is eaten by the police at last to destory the witness.these things is all in mary thinking.apparent,she has a canoots.
Take out her weapon from mary in the refrigerator (icy sheep leg), until she lets the police eat up sheep's leg finally, eliminate evidence, all these too at her disposal, very obvious, she is planned.