Complex sentence: The criminal charges were filed after an eight-year investigation by an animal protection group, Last Chance for Animals, which filmed over 72 hours of undercover video at Martin Creek Kennels, which included footage of dogs being shot.
Split into simpler sentences: The criminal charges were filed after an eight-year investigation by an animal protection group, Last Chance for Animals. The group filmed over 72 hours of undercover video at Martin Creek Kennels, which included footage of dogs being shot.