PUZZLEBOXX

If the delivery man needed help to move the crate then it was obviously heavy - so where are the contents of the crate?

You realise that the contents [which were protected by a plastic bag] must have disappeared.

You conclude that the man committed suicide.

He reached the hook by standing on a large block of ice that had been delivered in the crate. After he had jumped off, the ice melted - leaving no evidence, other than the wet patch on the floor that the doctor knelt in.