DURHAM, N.C. — A medical expert for the defense says Kathleen Peterson died as the result of a fall. On Tuesday, District Attorney Jim Hardin tried to pick apart the expert's testimony and started to raise questions about the doctor himself.

Forensic neuropathologist Dr. Jan Leestma said that he usually bills at $350 per hour. Hardin pointed out that $350 jumped to $500 an hour as long as Leestma is on the stand for the trial, adding up to $3,000 for Monday's testimony.

Leestma said he has no doubt Kathleen Peterson died from a fall down the stairs. However, prosecutors believe she was beaten to death by her husband, Mike Peterson.

Throughout the day, Hardin tried to hammer away at Leestma's credibility.

"When was the last time you actually performed an autopsy," Hardin asked Leestma.

"Maybe a year-and-a-half, two years ago," Leestma replied.

Hardin suggested that the neuropathologist was not qualified to offer his opinion about Kathleen Peterson's death. The neuropathologist admitted 90 percent of the cases he reviews involve children, not adults.

Hardin then pressed Leestma on a study of other fall cases. The neuropathologist looked at 257 deaths that involved blunt force trauma to the head. Leestma conceded Kathleen Peterson's death was unlike any of those.

Hardin asked Leestma to use a model of the staircase to show jurors how Kathleen Peterson could have fallen to her death. Leestma paused and then said he could not do it.

A crime scene investigator is expected to testify Wednesday and will talk about preserving the scene inside the stairwell. He is also expected to talk about blood spatter interpretation and how the blood stains at the Peterson mansion prove Kathleen Peterson's death was an accident.