Plot hole: Scar tells the pack he didn't make it to the gorge in time to help Mufasa. However Zazu was with them at at the gorge. He could have easily told Sarabi or any of the other lions on the numerous times he spoke with them, exposing Scar.
Suggested correction: Actually, Zazu wouldn't honestly say that Scar was lying; he left Scar at the gorge, but for all he knows, when Scar talks about not getting to the gorge in time, Scar could just mean that he couldn't find a safe path into the gorge to help Mufasa and Simba escape.
Suggested correction: Zazu wasn't with them when Scar said so. He was with Rafiki. He couldn't have heard what Scar was saying.
Suggested correction: But it wouldn't have confirmed that he killed Mufasa.
It would prove that Scar (who had the most to gain from Mufasa and Simba's deaths) was lying about the circumstances surrounding their deaths. But no-one brings it up.
It would prove Scar is lying about the events of Mufasa's (and Simba's presumed) death, and given Scar gained the most from it, the other animals should be extremely suspicious of him.
