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.
Additionally, Justin's lawsuit isn't just a defamation case. The original suit as filed contains 6 seperate charges against Murtha, and the statute of limitations may not apply to all or any of them. The amended filing may have more, I don't know. Here's a link to the original filing....
http://warchronicle.com/TheyAreNotKillers/LCplSharratt/Complaint_Sharratt_vs_Murtha_25SEPT08.pdf