Anyone know who SG's driver was? Was he a friend of hers or the date? Did she know him personally? Does he have a job other than that?
I know her BF traveled with her and did "other" things during that time, but did she previously know the driver?
The date and the driver could be the "they", and could make a tag team for killing prostitutes, drug addicts, etc... Could be just to not have to pay them, they may consider them a wasted life already.
There is your team. Call for a girl from out of town, pay for her to get there. Send driver to pick her up at hotel. Driver is your friend so no one will notice his car and appearance at your home with a girl.
That could explain strangulation to dismemberment, male and child. One was murdering first, before he met the other. They meet, get close, get high on something together, realize they both like the same things. Form a plan to keep it all from being local, and Wa La, tag team in small town, call for prostitutes from other towns, have fun partying, playing and killing together.