Sam arrives at Cassie's apartment with a bottle of wine to have dinner and talk about the case.
Cassie has not only made dinner, she's also cooked up a profile of the killer.
In sum: His "heart wasn't in it" (8.28); he'd never done this before (or he hasn't done this recently); he didn't want Katy to suffer; he only did it because he "had to" (8.45); Katy probably knew him, because otherwise she wouldn't have gone into the woods; and he probably only raped her to throw them off the right track.
Rob can't see how this case is connected with the old case, because serial killers don't usually take breaks. They don't get paid vacation… (Rob must not remember BTK.)
They bicker over whether or not Mark did it (for some reason, Rob insists that he did), but Cassie thinks his "faith" (8.108) would keep him from doing it.
Exhausting all the information, Rob and Cassie tell Sam about their backgrounds a bit, then Sam leaves and Rob crashes on Cassie's futon for the night.