During that conversation, the officials said, the officer allegedly said he would shoot the First Lady and then used his phone to retrieve a picture of the firearm he said he would use. It was not immediately clear what type of firearm was allegedly shown.
Police officials declined to identify the officer. Officials from the US attorney's office declined comment.
Police union chief Kristopher Baumann said he did not have details on the matter.
There was no indication of a legitimate danger to Michelle Obama. A Secret Service spokesman declined to provide further details, saying in an e-mail that the agency was aware of the incident and "will conduct appropriate follow-up".
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