LA CROSSE, Wis. -- The defense in the Eric Koula trial continued trying to convince the jury Wednesday that a professional killer was responsible for his parents' deaths. Koula is accused of killing his parents in their Barre Mills home in May 2010.

The defense called another expert witness to the stand Wednesday morning to testify the circumstances surrounding the murders were consistent with a professional hit.

The forensic specialist says that while a first-time killer typically leaves evidence at the scene, a professional usually does not. "I think it's an organized scene. I think it was well-planned, rehearsed, with experienced doers who knew how to do this type of thing and, most importantly, not leave any evidence," says Forensic Event Reconstruction Specialist Max Scott.

Scott also testified the nature of the shots that killed Dennis and Merna Koula were also consistent with a professional hit. He said the fact that there was one fatal shot per victim indicates an experienced killer.