Investigators tried Saturday to piece together what happened to a free-lance gemologist between her disappearance in February while carrying more than $500,000 in diamonds and her death less than a month ago. An autopsy on Barbara Mangiameli, 33, whose naked body was found Thursday floating in the Hudson River near lower Manhattan, showed that she died within the last month of a beating to the head. She was last seen at her Manhattan apartment building the day she was supposed to return six diamonds worth between $500,000 and $600,000 to their owner after a proposed sale fell through. Two brothers who allegedly arranged a meeting between a potential buyer and Ms. Mangiameli are in federal custody on charges they pawned one of the missing diamonds in Florida. They are not suspected in the murder because they have been in custody since April, and Ms. Mangiameli was then alive according to the autopsy. Ms. Mangiameli's body was covered by plastic bags and was bound in the fetal position by a Venetian blind cord around the neck, wrists and ankles, police said. An autopsy Friday found she died from multiple blunt force injuries to the scalp and face that caused skull fractures, brain contusions and brain hemorrhaging, said Ellen Borakove, a spokeswoman for the medical examiner's office. She was identified through dental records and an appendectomy scar, Ms. Borakove said. ``According to the doctor who did the case, she wasn't in the water for very long,'' Ms. Borakove said. ``She was not dead for a very long period of time from the time they found her yesterday. It certainly is not months. Whether it's weeks or days, I cannot pin it down.'' Ms. Mangiameli had worked for 10 years in advertising and two years ago went into the gem business. She recently graduated from the Gemological Institute of America Inc.