Who Stole the Dog? (Who Stole What from Whom? Part I)

A certain dog was stolen one day. Three suspects—Mike, Spike, and Slug—were rounded up for questioning. They made the following statements:
Mike: I didn't steal the dog.
Slug: I stole the dog.
Spike: Slug never stole the dog!
As it happened, at most, one of these three statements was true.
Who stole the dog?

(Source: King Arthur in Search of His Dog and Other Curious Puzzles by Raymond Smullyan)

This one actually falls to the first option: if Mike stole the dog, then Spike's statement is the only true statement here.