Yeah he was looking for a wire and according to real life taken from the book apparantly that did happen but with someone else checking and not Lefty. There are a few discrepancies like this.

The film is excellent, you can't fault the scriptwriters for that and yeah they did change a few events. But that's the film industry, I don't think the makers of this film were trying to make a true story but a dramatised story based on real events. They did a good job being able to put that into a 2hr movie.