examples of when conan doyle combines both elemts of detective skills and horror?

Answer 1

A number of his stories have an element of horror in them, when the unknown terrorizes the victims until solid detective work uncovers a much more logical explanation. "Hound of the Baskervilles" is the most famous example, when a supernatural killer dog is sent to hunt down a family and turns out to be a normal dog that has been trained to attack on command. Another is "The Scarlet Band," which turned out to be a poisonous snake that was secreted into the bedrooms of victims.

Answer 2

May I suggest that you read The Adventure of The Speckled Band.