It is a mafia investigation. alleged High level crime lord was wiretapped as was manafort. Alleged crime lord trying to stay alive by announcing to Semion he isnt cooperating with anyone.
The trick bere is to turn info gleaned from counterintelligence surveillance into “regular” admissible evidence. They are going to hit manafort hard in the indictment to get him to flip.
Renato mariotti who used to work in office taking down alleged crime lord lays out the intricacies of this investigation on a daily basis.
Btw...the fbi and their get pics of the expensives suits may have been about surveillance pics as pointed out by Renato.