I think it has been strongly shown that
if the prisoners are a population that may repeat interactions with each other then cooperators win out.
As I recall a game was played in a simulation. Different programs with different strategies were pitted against each other. Then the environment iterated with those doing well having more "babies". The wining strategy is:
Cooperate if not cheated.
Retaliate once if cheated and revert to co-opertation.
In other words be cooperative and forgiving. This wins against all comers.
In a single round there it is obviously best for both to remain silent. But the question is what is best for one to do? Unfortunately that may be to testify. Assuming you know nothing about the other person.