TL:DR on how was she killed?
Her body was eventually found naked and battered in a distant location, and the rental had forensic sings of having been cleaned of her blood. The sailor was recorded buying cleaning products at the same time, his DNA was found on her discarded clothes and her driving license was found in his cabin on the ship (along with a few pounds of hashish). A truly disturbed individual that tried to pin the murder on his colleague up until the very end.