Kellerman, Jonathan. Alex Delaware novels

Title from web page

"A much loved woman's dead body is found in her apartment, victim of horrendous overkill even as her dining room table is perfectly set for a romantic dinner. Turns out her devoted boyfriend has an alibi and, with few clues leading to a suspect, LAPD's Lieutenant Milo Sturgis calls in psychologist Alex Delaware for help. Then another woman's shot execution style; three bullets in the back of her head leave her husband with a profitable business. He's got an alibi too. As the body count builds, Alex and Milo make the horrible realization that they're dealing with a diabolically manipulative killer intent on playing the most twisted and bloodiest kind of game with the cops -- and with Milo, specifically"--