While it could very well be that TCS was a serial killer, and I will not rule that out either -- if he was not a serial killer than I do believe another male was involved here. Who and how remains to be seen -- but as they have separated Margaret and TCS -- they both are going to talk and we will see. In my mind there is a large chunk of this puzzle missing still. The folks that she worked with are most likely to know who would be partying with who and some likely scenarios if there was another person or persons involved. Cell phone records will also tell the tale.