Blood on an altar cloth covering a nun's body and DNA traces on her underwear did not come from the priest charged with her killing 26 years ago, a DNA expert testified Wednesday.

The DNA found on Sister Margaret Ann Pahl was likely from a man, but tests did not link the sample to the Rev. Gerald Robinson, said Cassandra Agosti, a forensic analyst with the state's crime lab.

Prosecutors said the trace of DNA was so small that tests showing it came from a man might have been wrong, or the sample could have been left by investigators on the scene or in the coroner's office.

Robinson, 68, was the hospital chaplain when Sister Pahl was found stabbed to death on the day before Easter, 1980. She was found in the chapel where both worked, but authorities have not disclosed a motive in her killing.

Investigators said Sister Pahl was not sexually assaulted, but her body was posed to look as though she had been.

Testimony Tuesday had focused on a silver, sword-shaped letter opener that was found in Robinson's room.

Detective Terry Cousino testified that he had never seen a letter opener like it, and said its shape was consistent with punctures in the altar cloth. He said mirror-image blood stains indicated the cloth had been folded in half over the nun's body.

Agosti testified Wednesday that the letter opener had on it a substance that may have been blood, but she said she could not prove it was blood.

"It could be a lot of things?" asked defense attorney John Thebes. Agosti answered yes.

Prosecutors pointed out that Agosti did not test the entire cloth when she determined blood stains that were examined did not come from Robinson.

But she agreed with Thebes that the tests show "he's not on it (the cloth)."

Prosecutors on Tuesday had showed the jury an enlarged photo of the letter opener inserted into the puncture wound in the 71-year-old Roman Catholic nun's jaw.

"The fit was so snug," said Julie Saul, director of the forensic anthropology lab in the Lucas County coroner's office. "It just seemed to lock into place."

The first autopsy done the day of Sister Pahl's slaying showed she died of 31 stab wounds to the face, neck and chest — including nine wounds that authorities have said were in the shape of an upside-down cross. There also was evidence that she had been strangled.

Robinson was a suspect early on because he was near the chapel at the time of the death. It wasn't until after his arrest two years ago and the exhumation of the nun's body that investigators discovered the puncture wound in the jaw.

Robinson, free on bail, could get life in prison if convicted of murder.