DURHAM, N.C. — The defense claims Kathleen Peterson died from a fall down the stairs. On Monday, a medical expert backed that theory.

Dr. Jan Leestma, a forensic neuropathologist, testified he disagrees with state Medical Examiner Dr. Deborah Radisch's findings. Radisch told jurors Kathleen Peterson's injuries proved she was beaten to death. Prosecutors believe Mike Peterson beat his wife to death with a blowpoke.

In a hearing outside the jury's presence, Leestma said he did not think a blowpoke could have been used as a murder weapon.

"The character of the wounds on the scalp are not consistent with that type of instrument," he said.

Leestma said the size, shape and placement of the cuts on the back of Kathleen Peterson's head were more consistent with a fall. He also believes the cuts came from an impact on a flat surface such as a wooden stair.

Leestma also said crushed thyroid cartilage found in Kathleen Peterson's neck may have been caused by moving her body after her death. Radisch had said the crushed cartilage was an indication that someone tried to manually strangle Kathleen Peterson.

Plus, the jury in the Mike Peterson trial has seen numerous pictures of the bloody stairwell where Kathleen Peterson's body was found dead. On Thursday, they are expected to visit the Peterson mansion to get an up close look at the stairwell.

The stairwell has been boarded up and preserved since Kathleen Peterson's death in December 2001. Her husband, Mike Peterson, is charged with her death. Defense attorneys want the visit to be the last thing jurors see before Dr. Henry Lee testifies.

Lee is a forensic scientist who is best known for his work on the O.J. Simpson case. He visited the Peterson mansion last year to study the blood spatter in the stairwell. Peterson's lawyers hope the visit will help put Lee's testimony in context.