According the the Affidavit, each of these abysmal characters have told multiple different versions of multiple different stories - so it's not clear exactly who did what.
It seems to me that this was predominately Cortney's plan, and that it's likely that she was the one who stabbed Rebecca in the truck while Bradly drove them out into the forest, and that Cortney then cut the baby out, with Brad holding Rebecca down. Afterwards they tied Rebecca's body to the bed of the truck to drag her off the road down an embankment.
They both report that the baby wasn't breathing when it was extracted (and they each appear to be unaware that newborns lungs are filled with fluid which generally needs to be cleared in order for them to breath). And they both report that they left the forest and drove back to the house and only then attempted CPR on the infant.
Michigan's laws for multiple parties implicated in the same murder are basically that if two or more people:
- plan the murder, or
- go together to commit it, or
- one holds the victim while the other kills, or
- one lures the victim, the other kills, or
- one drives the car, the other kills, or
- one cleans up the scene afterward as part of the plan
Both are charged with:
- First-degree murder (if premeditated)
- Conspiracy to commit murder
- Aiding and abetting murder
Punishment for first degree murder is
mandatory life in prison without parole.
--