What Would Have Happened...

No, you're right. Aaron Paul's character didn't realize it until later when he came back into the house & saw her in the living room. But they were in the news that day, in the newspaper & probably on tv when the power came back on. So even if they still didn't know they had tried to kill their daughter, they still could have found out they were wanted & called the cops. I guess the answer to these types of questions tends to be, "Because that would result in a very dull movie."

Again, they could have discovered it on tv or in the next morning's paper before everyone left. Neither likely, but it could have happened. Even if they hadn't, the investigation into the wrecked car & missing girls would have led straight back to the motel, where they were last seen. I assume the group was checked in under a fake name, but police would have realized the descriptions of the group whose room the car was parked directly outside of matched those of the missing felon & his accomplices, so they would know that the group was recently in that specific area & what kind of injuries they had to make them easier to id.

And yes, I know I've given this way too much thought. I just love this movie & have always wondered about this possibility...