Justin didn't file his suit until after his case was dismissed. The dismissal put the lie to Murtha and the date of the dismissal could be seen as the date of the injury, not when Murtha actually spoke the words. The dismissal was July '07 IIRC, and Justin's suit was filed in Sept. '08.
An interesting point. Not knowing statutory time limitation periods for PA, I suspect the is also a provision to toll statute of limitation periods for cases like this. Unfortunately, I seriously doubt that is is more than a few months after the tolled period ends.
As an example. If a normal case has a statute of limitations period of two years, but the criminal case took longer than two years after the defamation occurred, a party would be granted some period after the conclusion of the case to file a civil action. I seriously doubt that period of time did not lapse prior to Sharratt filing his lawsuit, but you'd have to check the PA statutes/rules on that.