Special counsel Robert Mueller's team is requesting that witnesses turn in their personal phones to inspect their encrypted messaging programs and potentially view conversations between associates linked to President Donald Trump, sources told CNBC.
Since as early as April, Mueller's team has been asking witnesses in the Russia probe to turn over phones for agents to examine private conversations on WhatsApp, Confide, Signal and Dust, according to the sources, who spoke on condition of anonymity.
Fearing a subpoena, the witnesses have complied with the request and have given over their phones, the sources said.
While it's unclear what Mueller has discovered, if anything, through this new request, investigators seem to be convinced that the apps could be a key to exposing conversations that weren't previously disclosed to them.
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A spokesman for the special counsel declined to comment.