Cornwell, Patricia Daniels. Scarpetta series.

Summoned to an unnerving, abandoned theme park to retrieve a body, Dr Kay Scarpetta is devastated to learn that the victim is a man she once loved. While teaching in Rome during the early days of her career, Scarpetta had an intense love affair with Sal Giordano that led to a lifelong friendship. The murder scene is bizarre, with a crop circle of petals around the body, and Giordano's skin is strangely red. Scarpetta's niece Lucy believes he was dropped from an unidentified flying craft. Scarpetta knows an autopsy can reveal the dead's secrets, but she is shocked to find her friend seems to have deliberately left her a clue. As the investigators are torn between suspicions of otherworldly forces, and of Giordano himself, Scarpetta detects an explanation closer to home that, in her mind, is far more evil