The mentally handicapped in 1944 Nazi Germany

I was rather surprised that Bruno was still at liberty .. in fact still alive - in 1944.
I was under the impression that all, (well, OK, large numbers) 'mentally subnormals' had be euthanised by the late 30's. Not only is Bruno 'out and about' in the community, but being fed, looked after, and fully aware of rights not to be blamed for things he did.
A large point if the film was that the higher authorities wanted to use this case to bring in euthanasia provisions.. I wouldn't have thought they needed 'excuses' by that late stage.
Would someone like to put me right on this?

few visible scars