NEW BRUNSWICK - A forensic expert says that he doesn't believe a blue blanket that's a key piece of prosecution evidence belonged to a woman accused of killing her 5-year-old son in 1991.

Defense expert Nicholas Petraco told a judge Thursday that there was a lack of trace evidence on the blue blanket, which was found in April 1992 by the boy's skeletal remains.

Three prosecution witnesses have testified that they saw the blue blanket in Michelle Lodzinski's apartment prior to her son Timothy Wiltsey's disappearance. The blanket had distinct metallic stitching on it.

Detectives say the blanket is key evidence because it is unlikely the boy was carrying around the large blanket at the carnival where Lodzinski said the boy was supposed to have disappeared. Detectives determined that the blanket must have come from the home and was used to wrap the boy’s body.

His remains were found in a marshy area in Edison a year after he disappeared.

The judge must now determine if jurors can hear the New York Police Department forensic scientist's testimony.

The Associated Press wire services contributed to this report.