When Michael and Sandy enter the house, he is carrying at least one of her high heel shoes. Hunter and McCall later see muddy footprints from both of her shoes on the carpet.
The stunt double used for McCall when she and Hunter were pushed down the steps is wearing darker pantyhose than McCall was wearing and was also wearing flat sole shoes. McCall had on high heels before and after the fall.
It makes no sense for Billy to keep trying to kill Sandy once the cops think the case is solved, and she didn't see or hear anything that could hurt him.
McCall was recording the entire time she talked to the bartender, yet was able to rewind the cassette tape to just the right point to only hear his conversation with Michael.