Friends and family were no closer to knowing what caused a prominent Orange County surgeon to be found dead in her swimming pool after an autopsy Monday proved inconclusive. The body of Dr. Marianne E. Cinat, 45, medical director of the UC Irvine Regional Burn Center, was discovered late Saturday morning by a close friend at Cinat's home in unincorporated Rossmoor, said Jim Amormino, a spokesman for the Orange County Sheriff's Department.Cinat, who was fully clothed, had been in the pool for more than 10 hours before the call came in at 11:15 a.m., he said. Nothing about the case stood out as highly suspicious, and further toxicology tests will determine the cause of death. Results will take five to eight weeks while the department continues its investigation, Amormino said.