maybe there were 2 killers.
extremely unlikely
A Six foot tall army sergeant wont need an accomplice in this situation.
The witness that night only saw the one man walking the street alone.
The witness described him very well.
The amount of money withdrawn form her bank card was the same amount of money he had to pay his landlord who he owed money.
It would be very difficult to find an accomplice to murder children and what for?
My conclusion is -
I don't think Hennis actually planned to do this in advance, Since he purchased the dog from her a few day before and knew her husband was going away, I think he went over there thinking he was gods gift to women and could bed her then she rejected his advance and he couldn't accept the rejection so went into a rage and raped her then killed all witnesses except the baby as she was to young to remember anything. This makes sense because Hennis is not a serial killer or suspected of any other murders and they get the urge to do it again. He probably got himself into a position of no return where by once he had raped her and realised the gravity of the situation he had to kill all the witnesses in order to get away with it.