How about someone who worked for a place like this:
Linds Custom Meats located in 172nd Ave, SE Kent in the South King Country area.
“We have a full service mobile slaughter truck that will come out to your farm or location.
…
All of the guts as well as the hide are then loaded into the kill truck and we then bring everything to the shop for disposal. We ensure that there is little evidence of a farm slaughter on your property!
January - September we are only able to schedule slaughtering appointments on Thursdays during the week.
Farm Butchering — Linds Custom Meats
The killer(s) could have murdered the couple several days earlier and driven the truck to collect them on Thursday.
The suitcases containing the body parts were found on a Friday.
According to the King County Medical Examiner's Office, the two victims were shot days earlier.
The ME would have given his opinion to the investigators as to the skill, if any, with which the bodies had been dismembered and the type of implement used. If it seemed even somewhat professional, I think LE would be checking Linds or any other similar company.
I'm sure there are many hardened criminals who couldn't bring themselves to dismember a body.