To start with, we shall have to spend a little time on the nature of conscience.
The Bible says that man is made in the image of God and when we are explaining what that means we stress that man like God is a moral being. He is able to reason, assess and respond at a moral level. He has a conscience which enables him to distinguish between right and wrong: to know the difference between good and bad.
No other created thing has this capacity and therefore it places man at the summit of God’s creation. It is this that makes man akin to God as no other creature is akin to Him. It is often said that a dog is man’s best friend. Personally I would want to challenge that, but accepting for the moment this idea, the very best dog has no conscience and quite definitely the very worst man has.