I have great difficulty believing in his innocence. The fact that he got rid of the mattress the next day alone proves he killed. I think his wife came home, went to bed and he strangled her, enraged to learn deceived or its affront to have filed for divorce.
Unfortunately it is neither the first nor the last who prefers to kill his wife rather than his ego.
Now he lives in lies for so many years that he can be self-confident to be innocent. It's still cynical to make money on the murder of his wife.