... and it turns out they have been reviewing Cohen's emails. There's the key source of the probable cause of criminal activity, which they will use as leverage.
"Fourth, the USAO-SDNY has specific reason to doubt that the seized materials will include the volume and nature of attorney-client communications that Cohen claims. This is because the USAO-SDNY has already obtained search warrants – covert until this point – on multiple different email accounts maintained by Cohen, and has conducted a privilege review of the materials obtained pursuant to those warrants. The results of that review, as resported by the USAO’s Filter Team, indicate that Cohen is in fact performing little to no legal work, and that zero emails were exchanged with President Trump."