Thanks Dudly! I've been doing some reading on decomp too.
At the time that the bodies were found, I'd guess that the coroner noted CR1's more advanced stage of decomp. Between lividity and rigor, they could probably tell that he'd been killed before the others.
My guess is that all bodies were in, what is called, the "Fresh" stage. The Fresh Stage, lasts 1-2 days. During that time of decomp, a lot of things happen, most internal from what I gather, except rigor and lividity. Lividity begins to work through the deceased within thirty minutes of their heart stopping and can last up to twelve hours. It may show as a dark purple coloring. Only up to the first six hours of death can lividity be altered by moving the body. After the six hour mark lividity is fixed. Livor mortis (lividity) is usually most pronounced eight to twelve hours after death.
Rigor begins throughout the body, but, normally appears to us, within two hours, in the the facial and upper neck and shoulder muscles. The deceased's face might take on what looks to be a grimace; this is because the facial muscles have contracted. Once the muscles have all contracted (8-12 hours depending on certain facotrs), the body will remain in rigor for up to 18 hours, after which, it will return to pre-Rigor condition. Putrefaction will start, and then the next stage, Bloat.
The next stage, Bloat, has a range of 2-6 days. I don't believe CR1 was that far advanced.
I believe CR1 had a more advanced state of Rigor. A couple hours. Maybe, BJM found them, much sooner after they were killed, than we think that she did. Instead of after 1 a.m., it may have been closer to the 3-5 a.m. mark. that they were murdered. IIRC
Mittens mentioned that KR would come to the trailer to shower, maybe that's the only reason he died, to give them more time before the bodies were found. It seemed they tried to hamper BJM finding them so soon.
Links used to summarize the above.
Decomposition – The Forensics Library
Rigor Mortis and Other Postmortem Changes - burial, body, life, cause, time, person, human, Putrefaction
Stages of decomposition | Tænketanken
Rigor Mortis and Lividity