Mr Groenewald of Humansdorp is missing. His wife suspects that he has been murdered. She contacts you to try find him. You suspect that your acquaintance, Piet, a car mechanic is involved. You contact him and ask him whether he knows anything. Piet informs you that the police are at his door. He hasn't told you anything over the phone except to ask you whether he should co-operate fully with the police. What would be your advice to Piet?