Sussman Trial - the beginning of the exposure of the biggest scandal in US History. Crickets, page-217

Correct, that's the process.

So, go ahead and bring in some of the people seen in the videos at the drop boxes and interrogate them.

As the "evidence" no longer exists (ie you can't recover what was placed in the drop boxes), you only have "the glare of the lights and in the inquisition" available to you.

Unfortunately, I don't think "enhanced interrogation" is still a possibility.