Night Moves by Jonathon Kellerman

An unhappily married couple (and  their 2 crabby kids) find a dead body with no head or hands in the father's home office. Since it's hard to identify the victim (with no dental or fingerprint clues), it's hard to know how he is connected to the family. Then the father turns up dead. Everyone's attention turns to an eccentric neighbor but Lieutenant Milo Sturgis and police psychologist Alex Delaware aren't so sure he's their guy. It's kind of a twisty story (in more ways than one) but a well-constructed mystery with an unexpected but logical resolution.