It is to fet them on something so that they can leverage that to get them to say things they might otherwise be unlikely to say. Ask them questions you already know the answers to, and when they lie, if you can’t get them on anything else, you got perjury to leverage.I dont. FBI has said in previous interviews they didnt believe the person was lying to them or intentionaly trying to deceive them but "special" prosecutors charged and sometimes got convictions anyways.
I think its all about adding to their list of names and they dont care about the pile of innocent bodies left in their path.
I was raised to always respect and obey the law and the police and have always done my damndest to do it but the older and more aware I become the more and more I despise government prosecutors.
There are some that still seem to operate with integrity. Sadly the ones that dont are sought out by politicians for their hit teams