A defense expert in the double murder trial of disgraced South Carolina attorney Alex Murdaugh testified Monday that he thinks two different shooters killed Murdaugh’s wife and son.While the idea has hovered over the trial because two different weapons were used and no evidence has been presented suggesting either victim tried to defend themselves, crime scene expert Tim Palmbach was the first witness to suggest the two-killer theory in testimony.Investigators have said 52-year-old Maggie Murdaugh was shot four or …