You may be looking for the Amos from Byzantium!.

Amos worked at a morgue near Sweetville. He identified several victims that were found in the canal had been afflicted by the "crimson horror". Looking at a glass containing some of the poison, Madame Vastra recognised the symptoms as coming from the red leech, 65 million years earlier. (TV: The Crimson Horror)

Community content is available under CC-BY-SA unless otherwise noted.