Q: Why do fingers turn black after death?

A: Post mortem black fingers mean one of two things:

1.) The victim died from exposure to the black plague.

2.) The Inker has escaped from Arkham Asylum.

The remains of the a fountain pen in the deceased's hand and the presence of a note by the body saying "I'm back to make crime in Gotham bold again" signed "The Inker" give credence to theory number 2, but the Black Plague is a serious matter and we'd be remiss not to examine all possibilities. After all, this is an election year.

I'll fire up the Bat Signal. You kill all the rats and poor people.