Complex sentence: Brianna tells McNulty that no one would have dared harm D'Angelo with Avon's protection and he speculates that D'Angelo's murder was planned or it would have been a swift shank.
Split into simpler sentences: Brianna tells McNulty that no-one would have dared harm D'Angelo with Avon's protection. McNulty specualtes that D'Angelo's murder was planned or it would have been a swift shank.