Here is what I'm thinking..
If it is a palm print and it could be shown to be Sheila's, it damages the police evidence with regards the cleanliness of her hands and as a knock on effect, the hand swab evidence.
If it is a palm print and it's shown to be JBs, he's toast.
If it is a palm print and it's shown to be June of Neville's, it means nothing.
If it is a palm print you'd better hope its Sheila's!