DURHAM, N.C. — A male juror brought his arms behind his head and yawned. A woman in the back row tried to conceal a smirk behind her hand, but didn't do a very good job of it. Other jurors wore blank stares on their faces, looking down only very rarely to make notes.

The cross-examination of a key prosecution witness during novelist Michael Peterson's first-degree murder trial Wedesday had the air of a Senate filibuster, but the questions and answers of blood spatter analyst Peter Duane Deaver are vitally important to the defense.

Attorney David Rudolf, who will face Deaver for a third day Thursday, does not seem particularly concerned about jurors' interest in his exchange with Deaver. Rudolf seems intent on getting the answers he wants for the record so that defense experts can later discredit Deaver's key conclusions.

Deaver testified Monday that, based on blood spatter interpretations and tests he conducted, he believes Kathleen Peterson was beaten to death in the stairwell of her home on Dec. 9, 2001.

Rudolf, who contends that his client's wife fell and hit her head more than once, continued questioning Deaver about experiments he conducted and videotaped. Jurors got a chance to see the tapes, but have heard differing views about why the tests were conducted.

Deaver insists that all the tests he performed at his laboratory at the North Carolina Bureau of Investigation were designed to see what sorts of blood stains would be created under different scenarios. For one, he dropped a weighted piece of styrofoam from 12 feet onto a piece of poster board. In another, he smashed a styrofoam head wearing a wig against steps in a full-scale replica of the staircase in the Peterson home where Kathleen Peterson died.

The defense played tapes of the experiments for the jury in an effort to show that Deaver's conclusions were not based on scientifically reliable tests. Rudolf also seemed to mock the experiments, including one during which Deaver stomped his foot in a small amount of blood from both standing and sitting positions.

For the most part, Deaver kept his composure under the barrage of questions about steps he did or did not take. But, at one point, he said he did not document one procedure because it would have been "attacked" like every other experiment he conducted and chronicled.

Jurors do not know it yet, but they will be sent home at the lunch recess Thursday so that lawyers can continue a hearing outside their presence that began Monday. The hearing focuses on the admissibility of 18-year-old evidence. Michael Peterson was the last person to be seen with a female neighbor who died in 1985 in Germany after falling down a flight of stairs.

Peterson, who lived in Germany with his first wife and two sons at the time, raised Elizabeth Ratliff's two daughters — then 4 and 3 years old — after Ratliff's death. Authorities attributed the death to a fall following a cerebral hemorrage, but prosecutors say a second autopsy performed in North Carolina this year found wounds consistent with a beating.

"I was always under the impression that Liz had a hemorrhage and had fallen down the steps and died," Cheryl Appel-Schumacher testified.

Although Appel-Schumacher did not recall anyone being suspicious of Michael Peterson, she noted a vague recollection that neighbors had questioned footprints in the snow outside Ratliff's home and whether all the doors in the home were secured.

"There was some kind of suspicion that things were not exactly the way the things were accepted," Appel-Schumacher said. "I didn't really suspect foul play ... It is fair to say I didn't suspect Michael Peterson of foul play."

Prosecutors hope to have jurors hear evidence about Ratliff's death. The defense, however, has argued that Ratliff's death is so dissimilar to Kathleen Peterson's that introducing evidence about an unrelated death 18 years ago will make it impossible for Michael Peterson to get a fair trial.

Martha Ratliff, whose natural father was killed in a military operation in 1983, is 21 years old now and still lives with Michael Peterson when she is not away at college. She showed no reaction in court Thursday when Appel-Schumacher broke down in tears while recalling her concern about what happened to Ratliff's "baby girls" when their second parent suffered an untimely death.

Testimony resumes at 9:30 a.m. Thursday. The trial is being broadcast by Court TV.