You all are missing TWO huge little problems. Just sayin...
This train of thought about how the blind man could have the girl kidnapped, and how the investigators could miss all the potential incriminating evidence in his house (both when responding to the panic alarm, or during the initial investigation when the girl disappeared in the first place) is all well and good, but my concern is with the gun store that sold a blind man a gun. Cash only and shady, or licensed & legit transaction, I would have serious concerns about who sells a big ol' revolver to a blind dude.
Just saying.
And seriously "Sorry Sir, I had my tubes tied three years ago" would have really been a buzzkill for him when she's in that weirdo-army-sex-swing.
This would have really flattened the intensity of the movie's tension.