The Death Collectors by Jack Kerley

In 1972, on the day of his sentencing, renowned artist and serial killer Marsden Hexcamp is shot dead in the courtroom. Members of his Mansonesque band of followers are imprisoned or simply disappear.

Fast-forward more than thirty years: A suspected prostitute is found murdered in a candlelit motel room, the first in a series of horrors suggesting Hexcampas art remains alive and treacherous. Following a trail of beautiful--and profoundly disturbing--artwork, homicide detectives Carson Ryder and Harry Nautilus descend into the shocking world of the Death Collectors, people who spend vast sums to collect serial-killer memorabilia. As Ryder and Nautilus race to solve a thirty-year conspiracy, it becomes sadly evident that at the intersection of art and madness, death is beauty, tragedy a memento, and suffering suitable for framing.