Mufasa's struggling in cklimbing up and Scar didn't help him instead he pushed Mufasa causing him to fell off from the cliff.
Long leave the king.
Help me brother.
Scar convince Simba to leave Pride Rock for blaming him of what happened to Mufasa but Scar is the one who kill his father. Scar told him that, what his mother would think after all happened. Simba doesn't know what to do so Scar told him to run away and never return. Scar sent three hyena to kill Simba but they failed and they don't told Scar about it.
I'm the responsible for my father's death.
Simba came back and schocked of the miserable situation Pride Rock. He fight Scar to recover his throne as a king. Scar try to distract him by reminding him of Mufasa's death and confessing that he kill Mufasa. Throughout the story the audince knew that Scar is the one who kill Mufasa,but Simba and the other Character doesn't know it.