I don't remember the author or the title but the plot involved a detective (FBI?) who specializes in serial killers, a serial killer who is killing mothers of young children, and a sub plot with a pair of serial killers who travel around in a van. The book theorizes that many serial killers are born devoid of human emotion and therefor must do these horrific things in an effort to feel something. These killers are referred to as 'Devoids'.
It was a very good book (scary!) and I would love to remember the name so I can buy a copy.

Thanks.