A doctor who says he helped a terminally ill woman kill herself cannot be prosecuted because authorities are unable to find her body, a district attorney said.

Authorities have reviewed the files of Dr. Timothy Quill, but said they could uncover no record of a myelomonocytic leukemia patient for whom the doctor claims he prescribed barbiturates and told her what dosage would cause death. He has identified the patient only as "Diane.""After not being able to identify `Diane' and after checking his records, there's no further way that we can go, in terms of being able to prosecute this case," Monroe County District Attorney Howard Relin said. "If you don't have a corpus delicti - a body - you don't have the potential for prosecution."

Quill, a general internist on the medical faculty at the University of Rochester, said "Diane" was his patient for eight years. County Medical Examiner Nicholas Forbes said he checked Quill's files and telephone calls accumulated over that period.

"We found no case that resembled this matter," Forbes said.

Relin said Quill's attorney told him the doctor would provide information about the patient only if granted immunity from prosecution.

Quill wrote in the March issue of the New England Journal of Medicine that he prescribed for "Diane" a large quantity of barbiturates. He wrote that he told her how much was needed for sleep and how much would cause death.