Peterson, 58, is charged with first-degree murder in Savio's 2004 death. The case was originally ruled an accident, but was reopened after Peterson's fourth wife, Stacy, disappeared in 2007.
Prosecutors have built a case on the theory that Peterson murdered Savio and made it to look like a drowning. Her body was found in a dried out tub in 2004.
The state has relied heavily on hearsay evidence, including the pastor of Peterson's missing wife, Stacy, who testified that Stacy told him she lied to police about the night Savio before Savio was found dead. Friends of Savio also testified that she told them Peterson threatened to kill her.
The defense, which began presenting its side on Monday, wants to cast doubt on the prosecution's theory and discredit the hearsay evidence. They called two pathologists on Tuesday in an attempt to do that.
Jeffrey Jentzen is a forensic pathologist whose 29-page resume was shown to jurors on Tuesday. He said, "It is my opinion that Kathleen Savio died from drowning, and the manner of death is accidental."
He said the injury pattern on Savio's body "classic for a fall" and that there were no defensive injuries that would have been the result of a struggle or assault.
"Individuals would typically fall backwards because of inertia and the muscle mass predominately in the back," Jentzen said.
"There has been reasonable doubt since the beginning of case that just adds more to it. This case is a bunch of Swiss cheese with holes in it. This doctor [was] powerful and concise," Joe Lopez, Peterson defense attorney, said.
Jentzen's conclusions directly counter the testimony of two other pathologists called by the state earlier in the trial. During cross-examination, prosecutors asked if it was possible Savio was killed, Jentzen said, "Anything is possible."
Prosecutors showed individual autopsy photos of bruises found on Savio's body that Jentzen said could have been caused by one fall. But Stacy Peterson's family spokesperson doesn't by it.
"There were over 13 bruises and abrasions that this doctor refused to acknowledge today," Pam Bosco said.
The jurors -- who continue to coordinate outfits and were wearing red, white and blue on Tuesday -- were then shown diagrams of how people generally fall.