Ok, put yourself in the failedmeister HKS's shoes.
Once he took on the Marshall vs Marshall pot of gold at the end of the rainbow case, HKS thought that he would make it big financially, career-wise, etc., fresh out of the water. He would be Mr. Big. His family and friends would look up to him.
With all the bips and bops taken by ANS and her handler HKS during the ins and outs of that case patience started to grow thin. Year after unsuccessful year not one single dime, no success garnered for HKS from that case.
All that HKS had gained in all these years was a D part in a not so popular tv series which is no longer on tv, an aging bisexual, prescription drug addict who was not attracted to him and who had the audacity to get pregnant. HKS sees most of his college friends have gone on and been successful. But not him, he reached the realization that he himself screwed the pooch (ANS's little puppy dog Howie). So he figures that someone has too pay.
Agree with your great summary!
Posted somewhere upthread that it would be interesting to find out if there are statistics on elapsed time between the decision to murder and the date of death.
i.e. Scott Peterson - decided to kill Laci 3 months(??) before Christmas.
Killing more than one person requires a lot more planning.