In this blog posting, someone called Judge Ellis is quoted saying, somewhere in America, some time recently or not so recently, in connection with something Trump-related, this:
“You don’t really care about Mr. Manafort’s bank fraud – what you really care about is what information Mr Manafort could give you that would reflect on Mr. Trump or lead to his prosecution or impeachment.
“This vernacular to ‘sing’ is what prosecutors use. What you’ve got to be careful of is that they may not only sing, they may compose.”
Good expression. Never heard it before, although it must have been around for decades.