(This is just my opinion and it is speculative based on a lot of online research in the area and my experience within the criminal justice system)
I believe it was someone who knew them, either through friends or family. Someone who worked with the girl’s parents. This perps are likely violent with a criminal past. I say that because if it was a drug related robbery, they had no reason to keep Jayme. It’s likely a sexually motivated for at least one perp and robbing them for the other(s).
Theory:
On the night of the crime, Perp 1 and perp 2 go to the Closs home. perp 3 (who probably works at Jennie-O's) is the lookout and lets 1 and 2 know when the father leaves the plant (Mr. Closs’ shift ended at midnight). perp 3 notifies 1 and 2, so they make entry into the house. The father clocks out at midnight, goes to his car, and drives home. He arrives and enters his home... at 12:31 (when neighbor hears shots) he is ambushed and killed by the perps inside. This creates a panic (probably) and a struggle ensues in which the mom is able to get away and hide in the bathroom. Perp 3 (who followed dad home from Jennie-O) grabs Jayme, while the other two go after the mother.
Between the perps who entered the house first and by the time dad came home, they were likely able to get some valuables...
They make their way either to MN, or somewhere in that area (all 3 of them most likely have lengthy criminal records in multiple counties, so they have plenty of hideouts).
the Cars likely arrived at the scene at different times, but were captured leaving together/ following one another.