Microscopic fibers found on the floor of David Westerfield's recreational vehicle are consistent with the carpet in the bedroom of his slain 7-year-old neighbor, a police criminalist testified Monday.

Prosecutors, whose capital case against Westerfield is now in its fourth week in a San Diego courtroom, allege that the 50-year-old engineer snuck into Danielle van Dam's family home during the night of Feb. 1 and snatched her from her bed. Searchers found her naked body three and a half weeks later by a roadside.

Westerfield listens to testimony Monday

The criminalist, trace evidence analyst Tanya DuLaney, also testified Monday that animal hairs recovered from Westerfield's RV, home and dry cleaning are similar to those of Layla, the van Dams' dog. Danielle's father, Damon, previously testified that the 7-year-old often wrestled with the Weimaraner before bedtime.

"They could've come from that dog," said DuLaney.

Westerfield lived two doors from the family, but the van Dams say they barely knew him and he had never visited their home.

DuLaney said she and other criminalists found blond hair similar to Danielle's in the RV. One strand was on the bedroom carpet near where police found Danielle's handprint, DuLaney said. Others were plucked from RV's sink and pillow cases and still others from Westerfield's bedroom, laundry and trash.

Danielle had a haircut six days before her abduction, and DuLaney said none of the hairs she saw was longer than 22 centimeters — the length after her haircut.

This testimony may prove crucial in the case. Westerfield's lawyers have suggested that Danielle may have played in the RV on a previous occasion, but witnesses say the RV was not in the neighborhood for weeks before the abduction.

A DNA analyst from the FBI lab testified last week that a hair from the RV's bath mat shared the genetic profile of Danielle, her brothers or her mother. Additional FBI analysts are expected to testify this week that other hairs came from Danielle.

During a cross-examination that stretched all afternoon and had jurors struggling to pay attention, defense lawyer Steven Feldman pressed DuLaney on the certainty of her findings. Feldman compared DuLaney's testimony that the hair and fibers were consistent with Danielle, her dog and her carpet to the DNA experts who conclusively matched the girl's blood and hair.

"Your opinion with regards to the carpet fibers is not an individualized opinion like the numbers for DNA," said Feldman, referring to one experts testimony that there was only a one in 670 quadrillion chance the bloodstain on a jacket of Westerfield's belonged to someone other than Danielle.

"Absolutely," DuLaney conceded.

The defense lawyer noted that the homes in the Sabre Springs neighborhood where the van Dams and Westerfield live were built at about the same time by the same contractor.

"A number of houses in the development could theoretically therefore have the exact same carpet," he said.

Yes, DuLaney said.

Feldman also grilled her about the hairs she linked to Layla. DuLaney said the gray-brown dog hairs were the same width and shared a distinctive "ovoid" pattern that allowed her to rule out police search dogs as the source of the hairs. She admitted, however, that she could not say with certainty that they were Layla's.

"Of course, they could've come from another dog?" asked defense lawyer Steven Feldman.

"Yes, that's true," said DuLaney. Later in the day, a veterinarian who DNA tested the dogs hair said the hairs did not contain enough DNA to yield results.

Feldman also quizzed DuLaney on the wide discretion she used in deciding which hair samples to send for further testing. In painstaking detail, Feldman reviewed hairs the criminalist found in Westerfield's home but decided not to test. DuLaney said she found almost 100 animal hairs in the RV, but sent only those that seemed likely to match Layla on for more analysis.

Similarly, she said, she found many hairs on Westerfield's belongings, but only sent certain blond or light brown hairs for DNA analysis. Other hairs, including some naturally blond and light brown, brown and white and others dyed blond and brown, she chose not to send for testing.

"You were only reporting out evidence that implicates Mr. Westerfield," charged Feldman. Judge William Mudd sustained a prosecution objection and ordered DuLaney not to answer, but later said her task was to find a link between Westerfield and the victim if one existed.

Earlier Monday, another police criminalist, David Cornacchia, said blood stains on a beanbag chair in Danielle's room showed a mixture of DNA profiles. Some clearly came from her older brother, Derek, said Cornacchia. Of the remaining DNA, some was unidentifiable and some consistent with the van Dams, but none matched Westerfield, he said.

Also Monday, Mudd told jurors they are not permitted to ask questions during testimony. The instruction came after one juror sent a note to Mudd asking when the panel could pose questions.

The jury will tour Westerfield's motor home later this week.