Manipulated? Sure. There's that one scene where they discover there was a hole in the blood sample. Of course there was a hole, how do u think the blood got in there?
Kid should have had a lawyer. Never talk to cops without one. Deny and lawyer up. Throw in his disability, the cops feeding him evidence and he's in the clear.
To me the question of whether they held stuff back concerns one scene and that's the crime scene. How could that bedroom be without any blood evidence?