Steve,
The questions being asked of Green are whether he knew that the porn was there,

He has answered that unequivocally. He says he did not.
That makes all your other questions pointless.

If the ex-cops are prosecuted he will not need to take any action.
I believe that if you bring a case for defamation the onus is on you to prove you are innocent. That would be impossible for him to do even if he is completely blameless.