Despite being making a good story, you can't actually get away with murder just by disappearing witnesses.
There are many instances where a witness statement may be read into evidence if the witness cannot be produced at trial. The most important of these is if the witness is dead, no proof of murder or the defendant's involvement is necessary.
Saunders states that Ms. Hagan is 5' 2" tall and that the railing was four inches under her chin, but the diagram of the boat shows the railing height as 4' 10". Since height is measured from the top of the head the measurements are off by a few inches.