"Marley was dead, to begin with."

[BlueSpot]

3. Here ya go

Dead as a doornail is a phrase which means not alive, unequivocally deceased. The term goes back to the 1300s, the phrase dead as a doornail is found in poems of the time. The term dead as a doornail was used in the 1500s by William Shakespeare, and in Charles Dickens’ A Christmas Carol in 1843. It is thought that the phrase dead as a doornail comes from the manner of securing doornails that were hammered into a door by clenching them. Clenching is the practice of bending over the protruding end of the nail and hammering it into the wood. When a nail has been clenched, it has been dead nailed, and is not easily resurrected to use again. An alternative wording of the phrase dead as a doornail is deader than a doornail.

https://grammarist.com/idiom/dead-as-a-doornail/

A doornail is, of course, a nail in a door. Don't you feel silly now?