The common law rule was that after a year and a day from the injury, it was no longer due to the crime. Since Brady lived to about the typical life expectancy for people of his birth year, this seems like a stupid and unnecessary complication in a case that's been over for decades. Having already been found not guilty by reason of insanity for the act, the State's hands are bound on retrying him for any additional charges now; they can't go back and revisit that just because one of the outcomes changed, even if you get past the causation issue.