Without giving away the ending, I'll say that this is my favourite Law & Order: Criminal Intent episode due to Goren's spectacular psychoanalytical roping in of the prime suspect, a psychopathological man completely lacking in the fear response and clearly narcissistic as well. It reminds me of the main character in the Grimm's fairy tale "The Story of a Boy Who Went Forth to Learn Fear."
Goren is always spectacular, but this particular episode really makes clear how brilliant a detective (and psychoanalyst!) he is. Having trained for 2 years in psychoanalytic theory in Switzerland at the C. G. Jung Institut, I can honestly say that this episode is the crowning glory of Law & Order: CI's psychologically-oriented storytelling. When Goren "goes in for the kill" at the end, he hits all of the marks of a good psychoanalyst who clearly sees the destruction, and yes, evil (otherwise defind as "unconsciousness") created by neurotic complexes in the psyche of Ken Harris.
I was rapt watching Goren close in on Harris and his masterful last words must rate as THE quote of all time on Law & Order: CI. Not to be missed for anyone interested in psychopathology and its devastatingly destructive effects.