Drowning has been determined the cause of the death of Phyllis Tharp of Por ter, for whom burial rites were held today, her 15th birthday. Coroner Carl Edmonds today sent his autopsy report to the county prosecutor's office which statedhat the young murder victim had suffered a skull fracture and fa cial injuries after being struck with fists and a stick by her assailant. ‘The accused youth, Patrick J. Watkins, remains in Porter County Jail after con fessing in a video-taped interrogation that he had confronted and assailed the girl a ‘Week ago at Lawson Lake, southal U. S. 20 in Porter, police said. The probable cause affidavit fued Wednesday in Porter Superior Court stated that Watson had said the girl was unconscious when she was thrown into the lake, once a borrow pit. Police received information Tuesday leading them to search for the body. Watson drew a map for sheriff's police and Porter Town Marshal Leonard Smith to show where he had last seen the girl. The body was found by scuba divers Tuesday evening.