Crime scene investigation

Someone's been sneaking biscuits from the biscuit drawer in the kitchen. After an exhaustive forensic examination of the crime scene using my trusty magnifying glass, I think I've found a clue to the culprit's identity. I've matched crumbs from the drawer with some I found on Daddy's lap as he was finishing his coffee ... looks like an open and shut case to me!

"There is always a pleasure in unravelling a mystery, in catching at the gossamer clue which will guide to certainty."
(Elizabeth Gaskell)