testimony optional

If Rosenstein grants UseImmunity,
then self-incrimination's not a threat.
Still, there's no end to human perfidy; 
it's hard to prove who's  feigning to forget.
Who knows what's in a perpetrator's head?
At best, we'll seize his 'phones, and documents--
and even those, he'd have been wise to shred--
an epistemic fine predicament!
But Mueller's trained to make the small fish squeal;
the last to find his tongue, will eat the loss.
The price of turning down the first plea-deal
may be a prison suite with his ex-boss.
A "prisoners' dilemma" for the books
when most key witnesses are likewise crooks.