This is my theory they are serial killers. All those people who died they all had one thing in common THEM.
They framed all those who were arrested (how smart are they) .
When her husband left her she went off the deep end, Thyme wanted revenge on the world!!!
Running into Rosemary who was screwed out of her job by an ex the banded together to wreck havoc on all plant, flower, and tree lover's.
Are you the same person who thought Del Griffith in "Planes, Trains, and Automobiles" was a serial killer?
shareHow true, sistermayhem31, but where they really shine is getting their victims to confess, sometimes adding corroborative details which even they had not considered. That takes real finesse.
However, I do question your assumptions about the cause. Laura was the gardener in the family (she and her father), her husband was a cop. Rosemary had been screwed out of her job by a former colleague who had recently become a department head at her University.
So, if your ideas about revenge were true, Rosemary and Laura would have been on a killing spree of people working in law enforcement and education.