https://arstechnica.com/information-technology/2018/06/fbi-recovered-hundreds-of-encrypted-messages-from-michael-cohens-phone/

In a letter to the presiding judge in the case against Michael Cohen, President Donald Trump's long-time personal attorney, the US Attorney's Office for the District of Southern New York revealed today that it had obtained additional evidence for review—including a trove of messages and call logs from WhatsApp and Signal on one of two BlackBerry phones belonging to Cohen. The messages and call logs together constitute 731 pages of potential evidence. The FBI also recovered 16 pages of documents that had been shredded, but it has not yet been able to complete the extraction of data from the second phone.

The letter to Judge Kimba Wood stated that "the Government was advised that the FBI’s original electronic extraction of data from telephones did not capture content related to encrypted messaging applications, such as WhatsApp and Signal... The FBI has now obtained this material."