NEW BRUNSWICK, N.J. — A state police forensic examiner acknowledged Thursday that five separate searches of Melanie McGuire's home failed to turn up blood or any other evidence of the gory murder and dismemberment of her husband.

The witness described how investigators and crime scene analysts returned to the townhouse repeatedly over a three-year period, each time employing new tactics, some of them extreme, in an attempt to find proof the slaying occurred there.

Thomas Lesniak, a forensic scientist at the police laboratory, said that, for one search, detectives moved the new residents of the home into temporary housing to facilitate a floor-to-ceiling examination of the property. During another, they vacuumed dust from air filters in search of fiber evidence. On another occasion, they unscrewed light fixtures to look for spots of blood and scraped up bathtub caulking in hopes of finding DNA.

Every attempt was fruitless, Lesniak conceded under questioning by a lawyer for McGuire.

"You looked thoroughly," attorney Joe Tacopina said.

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"Yes," Lesniak nodded.

"And you came up with no evidence," the lawyer said.

"That is correct," Lesniak replied.

The lack of forensic evidence in the home is the defense's strongest argument for McGuire's innocence. In 2004, her husband, William, was shot three or four times and carved into pieces with a power saw. His remains were wrapped in garbage bags, stuffed into the family's set of luggage and dumped into the Chesapeake Bay.

McGuire, 34, claims she last saw her husband when he packed his belongings and stormed out of the apartment following a violent argument. Her defense has implied he was killed in Atlantic City because of alleged gambling debts.

The investigative effort described Thursday by Lesniak and two other witnesses, another scientist and a medical examiner, appeared intensely focused on finding some piece of evidence, no matter how small, that would establish the home as a crime scene. The searches continued until last September, almost a year after McGuire's arrest.

Lesniak said on two occasions, officers used the chemical Luminol, which detects blood, but with no positive results.

"Blood is hard to wash away," Tacopina said.

"It's not that hard," Lesniak protested.

"If they do a lousy job cleaning up, sure you are going to be able to spot it," the lawyer replied.

Lesniak shrugged and remarked, "We do it every day in the lab with our tables."

Still, he agreed, it was not only blood that was absent. He recalled another search of the house in which he scoured the porcelain in the bathtub and shower for nicks that might have been caused by a saw. He found nothing.

Another lab employee said investigators initially thought they had found blood in the runner of the shower when presumptive tests came back weakly positive. DNA tests, however, showed it was not blood.

A medical examiner told jurors he had gone to the townhouse to examine a refrigerator to see if William McGuire's body may have been stored there before being thrown in the bay, but found the interior of the appliance did not have enough distinguishing marks to compare to marks on the victim's body.

Lesniak was called to the stand by prosecutors Wednesday to describe testing he performed on some 200 items, including garbage bags from the defendant's house which he said were identical to ones used to dispose of the body.