Keeping it fresh--murders, that is

Right now I'm writing my third in the Matti James Mystery series. In each, there is a different manner of death. Each creates a problem for the forensic facial reconstruction artist and each is solved using techniques that are not fiction. For example, CT scans can be run through a computer program to compress the slices. That "solid" image can be turned into an exact plastic replica by a 3-D printer. Technology aside, I hope I make my killers interesting --driven not by mental defect. That's too easy an out. My late cousin was an FBI trained police psychologist and worked with profilers. His notes give me interesting avenues to investigate.