CONCORD, N.H. (AP) — Prosecutors objected Thursday to claims by lawyers for a teen-ager accused of killing two Dartmouth College professors that forensic evidence in the case is unreliable because the state police laboratory is not accredited.

The motion filed by lawyers for Robert Tulloch, 18, does not cite any specific case in which the Concord lab has produced flawed tests.

If there were any past mistakes, defense lawyer Barbara Keshen, a former state homicide prosecutor, should be able to cite them, Assistant Attorney General Kelly Ayotte said in court filings.

Forensic evidence, particularly DNA evidence, is a central part of the prosecution's case.

The lab is not nationally accredited by the American Society of Criminal Laboratory Directors. But Ayotte said the state lab technicians are qualified scientists.

Thirty to 35 states and nearly every federal crime laboratory are accredited, according to the American Society of Criminal Laboratory Directors, a national accreditation agency.

Tulloch is charged with first-degree murder in the slayings of Half and Susanne Zantop, who were stabbed to death last year in their Hanover home.

Tulloch plans to use an insanity defense. His friend, James Parker, has pleaded guilty in the death of Susanne Zantop and agreed to testify against Tulloch.