Notably, one of the most important revelations in is that Sirius Black is an innocent man, and the real enemy who ratted out Harry's parents is Peter Pettigrew ( reveal this, but it does so rather chaotically.

Source: https://collider.com/prisoner-of-azkaban-best-directed-worst-written-harry-potter-movie/

Not only had isolating Harry been a bad idea, but Dumbledore forcing Sirius Black to stay at Grimmauld Place had only ensured that the man would take off at the first chance.

Source: https://screenrant.com/harry-potter-order-phoenix-dumbledore-book-confession-cut/

Now the caring son wants to do something for another treasured family member - their dog, Sirius, who was named after the Harry Potter character Sirius Black.

Source: https://www.coventrytelegraph.net/news/uk-world-news/son-caring-dying-dad-burst-27553487