He is NOT going to get off for this reason. The most they can do is have his comments made during this period ruled inadmissible. It appears highly likely there is a great deal more other evidence than necessary to convict him. We don't need a confession.
One of the first questions from a reporter after his capture was if he had been marandized and it has come up several times since...If you don't think one or more lawyers represnting him isn't going to make that an issue you are way too naive.