bloodhound

Short definition from Wiktionary

Noun

1. 1
   A large scenthound famed for its ability to follow a scent many days old, over vast distances. This dog is often used as a police dog to track missing people, fleeing suspects, or escaped prisoners.
2. 2
   A detective or other person skilled at finding people or clues.
3. 3
   A bloodthirsty person.