It was a trial to remember on Prince Edward Island, Canada. A young woman was murdered, her estranged boyfriend was accused of the crime, and the main evidence against him came from the DNA of a cat.

Forensic scientists say the case is the first in which animal DNA has been introduced in court. It came about only because a determined police officer searched until he found a researcher specialized enough to perform the needed analysis.

''Without the cat, the case falls flat,'' the defense lawyer, John L. MacDougall, told the jury. But after hearing testimony about how DNA was obtained from the hair of the family cat, the jury found the accused, Douglas Beamish, guilty of second-degree murder.

The case, decided on Aug. 1, is reported in today's issue of the journal Nature.

It began on Oct. 3, 1994, when Shirley A. Duguay, a 32-year-old mother of five, vanished from her home in Sunnyside, a city of 16,000 that is the second-largest city on Prince Edward Island. Her car was found a few days later, splattered with her blood. Several months later, Ms. Duguay's body was found in a shallow grave.