DURHAM, N.C. — Kathleen Peterson's stairway collapse was no Hollywood stunt, but she hit just about everything on the way down, according to the defense expert who testified Wednesday in Michael Peterson's trial for her murder.

"This is not a Hollywood tumbling fall down the steps," said Faris Bandak, Ph.D., a biomechanical research scientist who works for the Department of Transportation.  "I would venture to say this is a ground-level fall."

The "ground-level fall" was a new layer in the fall theory advanced by Peterson's defense team.  Jan Leestma, a forensic neuropathologist, and Henry Lee, a forensic scientist, both testified on Peterson's behalf that Kathleen Peterson fell at least twice on Dec. 9, 2001, and could have slammed her head more than once with each fall.

Biomechanical researcher Faris Bandak testifies Wednesday

Bandak, who plugged Peterson's weight and height into some physics equations, theorized that Peterson was walking up the staircase when she fell backward and her head struck a ridged molding on the door jamb. In his theory, as she fell to the floor, her head may have grazed the wall before impacting the edge of a stair. She then must have attempted to stand up, but slipped and fell backward once more, again with potential multiple impacts.

Prosecutors say they have a simpler explanation: Michael Peterson beat his wife of five years to death, and made the murder look like a fall.  Peterson, 59, could spend life in prison if convicted of first-degree murder.

Trained in applying physics and mathematics to injuries, Bandak used Peterson's height and weight along with the dimensions of the stairwell to calculate how two falls, each with multiple impacts, could have caused the wounds she sustained.

"We know that the fall height had to be less than what it takes to cause a skull fracture, but more than what it takes to cause laceration," said Bandak.

The characteristics of the lacerations on Peterson's head — prosecutors count seven of them, the defense counts only four — rule out bludgeoning by a rod-like object, said Bandak.

"Were you able to form an opinion ... as to whether Kathleen Peterson's injuries were the result of her being beaten in the head with this blowpoke, or a blowpoke like this," asked defense attorney David Rudolf, holding up a fireplace tool like that prosecutors have singled out as the murder weapon.

"Yes, the biomechanical evidence and her injuries are not consistent with that kind of force," said Bandak.

"Do you have an opinion what the cause of these injuries were?" said Rudolf.

"I believe from the scene data and Kathleen Peterson's dimensions that her injuries were caused by an accidental fall in that stairwell," Bandak replied.

And the bruises on Peterson's arms could have been caused by her backward fall as well, he said.

Part of the expert's presentation included a computer animation of his scenario, showing a hairless female figure (which, oddly, sported black nail polish although it wore no clothes) reeling backward and striking the doorjamb.

The dramatic 15-second animation could help jurors visualize a fall scenario, or it could convince them that the defense's explanation is just too complicated to swallow.

Despite his assurance that he was confident beyond a "reasonable scientific margin" that Kathleen Peterson died in a fall, Bandak had trouble explaining why the victim had facial bruising.

Pressed by the prosecutor, Freda Black, Bandak said his reconstruction was only a "likely scenario," suggesting that she could have hit the edge of a stair with the front of her face as well.

He also became combative when Black asked whether he'd ever done research himself on fall injuries.

"Do I have to build a 707 to fly in one?" he snapped.

Black also pressed Bandak on whether he had created a scenario that neatly fit the defense's theory. The expert, who at times appeared uncomfortable on the stand, said that he merely constructed a possible scenario based on the physical characteristics of the scene and the victim. 

Bandak used a barrage of metaphors on Wednesday, comparing different facets of cranial anatomy to, at various times, a carton of orange juice, Jell-O, a balloon full of water, glass, a tent, a wishbone, a diving board, a Halloween mask and a set of steel balls, one small, one large, bouncing off each other.

Earlier on Wednesday, Bandak, who said he'd visited Peterson's Durham home six times and had billed $40,000 in the case so far at a rate of $500 per hour, explained that Peterson's head could have sustained so many apparent lacerations because, like a windshield hit with a pebble, the impacts to her head created a complex spider web pattern. 

Black asked him to elaborate during her cross-examination on his theory about the lacerations.  Asked to count them, Bandak appeared flustered, saying first that there were four, then that there were seven, and finally calling the number of lacerations simply a matter of "bookkeeping."

Bookkeeping or not, the lacerations remain one of the strongest pieces of evidence put forth by prosecutors.

Judge Orlando Hudson Jr. gave jurors Thursday off, citing the approach of Hurricane Isabel, and said he would take his cues from local school districts on whether to resume court on Friday. 

Peterson's trial is being broadcast by Court TV.