The code..
...which was found on Morten's fridge door, leads to Claes. It was identical to the EMail address he sent to the photographer when he commissioned her to take pics of Freddie's wife.
If so, then that would identify him as Morten's "brother" and his killer. Perhaps they were in the military together, but I can't make a connection to the foster homes.
We do know that he "killed" his father.