The museum of desire By Jonathan Kellerman.
"Psychologist Alex Delaware and detective Milo Sturgis struggle to make sense of a seemingly inexplicable massacre in this electrifying psychological thriller from the #1 New York Times bestselling master of suspense. LAPD Lieutenant Milo Sturgis has solved a lot of murder cases. On many of them--the ones he calls "different"--he taps the brain of brilliant psychologist Dr. Alex Delaware. But neither Alex nor Milo are prepared for what they find on an early morning call to a deserted mansion in Bel Air. This one's beyond different. This is predation, premeditation, and cruelty on a whole new level. Four people have been slaughtered and left displayed bizarrely and horrifically in a stretch limousine. Confounding the investigation, none of the victims seems to have any connection to any other, and a variety of methods have been used to dispatch them. As Alex and Milo make their way through blind alleys and mazes baited with misdirection, they encounter a crime so vicious that it stretches the definitions of evil"--Provided by publisher.