In April, the FBI raided Cohen’s law office and hotel room, seizing boxes of documents, phones, electronic devices, and computer equipment.
At a recent court hearing, prosecutors said they were still sorting through the material and needed more time to piece together the contents of a shredder and gain access to a BlackBerry.
Even before the raids, federal investigators had been monitoring Cohen’s phone lines, multiple senior officials and individuals with knowledge of the legal proceedings have told NBC News.
The calls were logged by what is commonly referred to as a pen register, which records the number of the phone that made the call and the number that received it, but does not record the contents of any conversation.
Cohen has denied wrongdoing.
A longtime Cohen business partner agreed in May to cooperate with the government as part of a plea deal, according to a person with direct knowledge of the proceedings.
Evgeny Freidman, 47, a disbarred lawyer who is known as the “Taxi King,” pleaded guilty to a low-level felony in Albany County Court, in upstate New York, for stealing nearly $5 million in state taxes and agreed to cooperate in state or federal investigations.
For years, Freidman, a Russian immigrant, has managed Cohen’s taxi medallions, which give owners the right to operate New York City yellow cabs. Multiple people familiar with the proceedings would not say if Freidman’s cooperation was specific to the ongoing federal criminal investigation into Cohen.