The definition of "dynamic character" states that such a character is one who undergoes some inner change through the course of the story. A dynamic character attains some new understanding of life, overcomes some important hurdle, achieves some daunting task, realizes a mistake or mistaken notion or outlook, resolves a major personal conflict between opposing points of view (should versus ought; need versus want, etc). Dynamic characters are often not found in adventure stories, action stories, science fiction stories or other genre specific stories including romance stories (although good romances will always include dynamic characters) because the objective of these stories is to experience the adventure, survive the action, explore and conquer the science fiction, win the heart of the gal or guy. Dynamism of character is not always required or wanted for these objectives.
Shelter is the antagonist (the villain) of a murder mystery horror novel, which already sets up two reasons to expect that Shelter will not be a dynamic character. Working backwards, first, the genre combines three minor specialized genres that typically focus on objectives other character dynamism, as discussed above, therefore Shelter is not expected to be dynamic character (a character who undergoes positive inner change). Second, Shelter is the antagonist. Dynamic characterization is usually reserved for the heroes and minor good guy characters, for instance Mr. Bingley in Austen's Pride and Prejudice who undergoes a minor dynamic change when he comes to realize he relies too heavily on Mr. Darcy's opinion. Therefore, since Shelter is the antagonist, there is no expectation that he will be a dynamic character, which makes it more cathartic (novelistically satisfying) when he gets his just desserts.
In point of fact, Shelter does fulfill both expectations. In terms of the genre, Shelter has no impetus to have dynamic character change. In terms of his character role as antagonist, Shelter has no motivation to undergo dynamic character change. Shelter therefore is not a dynamic character. He is in fact a static character.