New York (CNN) In most respects, Michael Cohen was a frustrating witness for New York investigators.

He toyed with, but wouldn't commit to, "full cooperation" with prosecutors, according to court filings. He refused to tell them about crimes for which he hadn't been charged. He wouldn't meet with them about "other areas of investigative interest." With officials in the state attorney general's office, he provided only corroboration for what they already knew, and with the state tax department, only what investigators could have obtained with a subpoena or two.

But there is one probe in the Manhattan US Attorney's office for which President Donald Trump's former personal attorney has proved helpful, according to court filings and people familiar with the matter: The investigation of the Trump Organization. That probe, and Cohen's participation in it, poses one of the most significant threats to the President's family business.

The investigation has been underway since before Cohen was first charged in August, CNN has reported, and is the subject of an ongoing grand jury investigation. The inquiry stems from the original campaign-finance charges against Cohen for making or orchestrating payments during the presidential campaign to silence women -- adult-film actress Stormy Daniels and former Playboy model Karen McDougal -- who claimed sexual encounters with Trump. (Trump has denied those claims.)

In the court papers filed against Cohen in August, and again last week, prosecutors referenced several unnamed Trump Organization executives and employees who directed or participated in a scheme to reimburse Cohen for the payments, and prosecutors have been examining whether people within the company should be charged as part of that effort.

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