The headline is technically grammatically correct but ambiguous. “…shot and killed unarmed black man” would have been better. If you absolutely need to stick to word/character count, “shot unarmed black man dead” would be less ambiguous and more in keeping with how people actually use “shot dead”. I’ve watched a lot of westerns and I can think of quite a few where someone says “I shot him dead” but not one where someone says “I shot dead him”.