What evidence convinces the police that Sal killed Andie?

The police find out that Sal got his friends to give him a false alibi, and that his father got a text from his phone seeming to confess to the crime. When the police find Sal, he has Andie's phone with him, and there are traces of her blood under two of his fingernails. Andie's blood is also in the trunk of her car, and Sal's fingerprints are on the steering wheel and dash of that car.