Back at the lab, Calleigh and Horatio are reconstructing Stephanie's death, putting up a wooden frame and plastic sheeting to catch the detritus and packing a rifle with plenty of powder to simulate its kick upon firing. Calleigh positions a dummy, saying, "Usually suicides lean forward to get a better shot." Horatio muses, "That would create spatter directly above, but in this case, the blood is back here, so she needs to be back." Calleigh positions the dummy so that she's reclining on the couch. Mmmm, napping on the couch. I could get behind that. Horatio then leans down between the dummy's knees, positions the rifle, and fires it. Sure enough, it spatters to the back. After a loving close-up of the plastic carnage -- which really isn't an improvement over Stephanie's face -- and the confirmation that Calleigh used boiled noodles to simulate brains, the two conclude, "She's either the most relaxed suicide on record, or she was taking a nap." Well, there goes your Mom-goes-on-a-killing-spree theory, because how's she going to pull the trigger while napping? Someone else shot her.
Minutes later, Delko is pulling out Speedle's stenciled carnage diagram and saying, "The blood on the blanket in the doghouse proves the toddler was there after someone was injured." Horatio says, "Right, but her feet were drenched with the blood of all five victims, though." Speedle corrects him: "Not until after she was hiding in the backyard. The transfer from the blanket came from one bleeder -- her mom." And the Mom-on-a-spree theory has one more nail driven into it. I hope Horatio's prepared to grovel when he breaks this news to Stephanie's sister; I hope he breaks it to her, period. I also hope that maybe some of the other CSIs stop and think about how they have broken Olympic records in the Long Jump To Conclusion. Clearly, I'm hoping in vain. Anyway, Delko and Speedle conclude that there's no chance Erin got to the doghouse under her own power; someone carried her out there. Horatio orders the boys to find out who had glyphosphate and soil on their shoes. Both Luke and Jason do, so the next step is to see which one of them is capable of carrying the toddler out, and which one is likely to have snapped and begun murdering his family members.
Speedle's doing his part by checking the clothes for bloodstains while Calleigh watches; I get the feeling from their interaction that she's looking to pump him for as much lab savvy as he's got, as she's usually asking him questions and not vice versa.