DURHAM, N.C. — Defense attorneys for Michael Peterson, charged with killing his wife and making her death look like a fall, challenged how police supervised the death scene, during the novelist's murder trial Thursday.

Nearly half an hour after one police supervisor arrived at the Peterson's home to find Kathleen Peterson dead at the bottom of a staircase, she told another senior police officer that she believed they were dealing with an elderly woman who had gotten up from a wheelchair and fallen down stairs.

Michael Peterson

That initial assessment of the scene, from Corporal J. C. McDowell, is notable for its inaccuracy: 48-year-old Kathleen Peterson did not use a wheelchair.

In its cross-examination of McDowell, the defense was aiming to show that, from the start, police didn't know what they were doing. They also drew out the fact that police failed to keep people from contaminating the scene because they thought they were dealing with a fatal accident.

McDowell, the prosecution's 12th witness over seven days of testimony so far, explained that she was merely repeating to another supervisor what she had been told or heard inside the Peterson home. Although she summoned crime scene technicians and detectives, McDowell admitted that yellow police tape and other basic measures designed to preserve scene integrity were not put in place until Corporal Scott Kershaw arrived at 3:18 a.m. and briefly took command.

Kershaw said he posted an officer at the front door to block access to anyone but investigators and instructed the officer to write down the names and times of people crossing the threshold. Defense lawyer David Rudolf used that log book to show that police were going in and out of the home frequently, including senior commanders who had no duties that required them to be inside.

Corporal Scott Kershaw

"There's a lot of people in that scene that night, correct?" Rudolf asked.

Kershaw agreed that there was a lot of traffic and that he issued the orders because they were needed to control the scene.

The integrity of the crime scene is likely to become crucial to the defense later in the first-degree murder trial. Prosecution witnesses are expected to testify that finding blood in unexpected places was one of the reasons they decided Kathleen Peterson's death was a homicide, not an accident.

Some blood spatter, for example, was found more than six feet above where Kathleen Peterson's body was found at the bottom of a staircase.

The defense contends that the blood was found in such unusual places because of significant scene contamination. One officer walked right through the hallway where Kathleen Peterson's blood-soaked body lay.

McDowell testified that when she used a cordless telephone handed to her by Todd Peterson, the defendant's son, to call superiors she violated standard protocol. The defense maintains that Todd Peterson reached into the stairwell in the presence of police and grabbed the same cordless phone Michael Peterson used to call 911.

Just before court recessed for the day, police Sgt. Terry Wilkins testified that he summoned one of the Durham police department's most senior commanders to the scene when he realized that the victim's husband was Michael Peterson and that the case might take on a high profile.

The defense has not cross-examined Wilkins yet, but his testimony could play into another defense stratagem. Peterson's lawyers assert that Durham police may have been biased against him because he wrote newspaper columns critical of the police and often complained about police coverage in his neighborhood.

More police officers are expected to testify in coming days before prosecutors call pathologists to the witness stand. One pathologist initially concluded that Kathleen Peterson's death was consistent with a fall but changed his mind after an autopsy disclosed seven distinct lacerations on the back of her head.

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