NEW BRUNSWICK, N.J. — A forensic examiner told jurors at Melanie McGuire's trial Wednesday that garbage bags removed from her residence were identical to those wrapped around her husband's dismembered body when it was pulled from the Chesapeake Bay.

The witness, a forensic scientist at the state police crime laboratory, said a distinct pattern of swirls and lines in the oversized black plastic bags meant they were made in the same factory and by the same machine.

"It's kind of like a fingerprint of the extrusion," Thomas Lesniak said, referring to the industrial process for forming the bags.

He told jurors that "chads" — small perforation marks at the top and bottom of the bags — were in "perfect orientation" and that a slight bump on the upper edge of every bag was proof that they were all sliced with the same, slightly deformed blade.

Prosecutors, whose case against McGuire is built entirely on circumstantial evidence, have placed special importance on the garbage bag comparison. Other evidence, including hairs, connects McGuire, a 34-year-old fertility clinic nurse, to the three suitcases containing her husband's remains. But because the McGuires used the luggage for travel, the hairs' presence has an alternative, benign explanation.

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The bags, however, have the potential to link the defendant not just to the suitcase, but to the dismemberment of her husband. William McGuire's body was cut into four pieces with a power saw before being placed in the bags.

"This is a very significant case for the state," Assistant Attorney General Patricia Prezioso acknowledged in comments to the judge Wednesday.

Prosecutors intend to call a second expert, a scientist who works for a plastic bag company, to detail chemical similarities between the two sets of bags.

In a hearing in January, prosecutors said Lesniak was prepared to testify that the bags from the bay were manufactured within 20 bags of those containing the clothes. State Superior Court Judge Frederick DeVesa barred that testimony, however, because it was based on interviews the scientist did with others concerning the production process.

In May 2004, the week her husband's remains were identified, McGuire gave six bags of his clothing to the cousin of a friend. The young man previously testified that McGuire intended to throw out the garments, but gave them to him after he helped her move. Police later seized the bags.

Lesniak set up a light box in the well of the courtroom to demonstrate his analysis of the bags. Jurors craned their necks as he draped one of the bags over the box and pointed out marks made by dye. The heavy-duty plastic bags measured 35 inches by 39 inches and were of the type used to collect leaves, Lesniak said.

He used enlarged photos to show similarities between the two sets of bags.

"This is your dye line. You can actually see how it goes from one bag to the next," he told jurors.

He said he also compared a bag from the home of McGuire's parents and found the same similarities.

Lesniak's presentation prompted state Superior Court Judge Frederick DeVesa to warn jurors against conducting their own experiments.

"Please don't go home tonight and hold up any bags in front of a window or light," he said, prompting giggles from the panelists.

Lesniak also testified that he found a microscopic paint chip consistent with red nail polish on a piece of duct tape on the exterior of a suitcase containing the victim's head and upper torso.

His testimony is to resume Thursday morning. The trial is being streamed live on Court TV Extra.