His personal lawyer went to prison for 2 years on charges related to this crime, and was the primary witness against Trump in this Grand Jury investigation.
Whatever he told them, along with whatever other evidence was presented, it was sufficient for them to indict.
They had better have some pretty solid evidence aside from his testimony. Building a case around the word of a man convicted of perjury, especially one with a public hatred of the defendant, seems like a profoundly stupid thing to do.
I'll be waiting with my popcorn, because one way or another, this is gonna be good.
The relevant phrase in the Michael Cohen indictment referring to Trump was "unindicted co-conspirator". Individual one is how they referred to him. Trump was supposed to be featured much more prominently in the indictment, but the Barr's DOJ intervened on Trump's behalf to minimize his presence in the proceedings, and they went out of their way not to mention him.