A dispute over DNA testing is slowing prosecution of a southern Illinois man who is accused of setting a house fire that killed four children.  The Southern Illinoisan reports Randolph County State’s Attorney Jeremy Walker says state police testing of evidence may destroy some of the potential trial exhibits in the case against Derrick Twardoski.  Twardoski’s public defender is James Kelley, who objects to that claim.  Randolph County Circuit Judge Richard Brown has scheduled a hearing for Thursday to decide the matter.  33-year old Twardoski has pleaded not guilty to four first-degree murder counts in the deaths last May in Percy, near Sparta.  The fire killed siblings ages 12, 9 and 5-year old twins.  Their parents and another 6-year-old escaped.