A leading US free-expression group has hit out at federal prosecutors’ use of a novel written by former FBI director James Comey in their case accusing him of threatening to kill Donald Trump.

“Citing a novel to save an indictment that is constitutionally dubious is a desperate Hail Mary and should be rejected,” said a statement posted on Friday by Mara Gassmann, legal director of PEN America, using a term for a last-second heave in American football.

Prosecutors with the Trump administration-led justice department had argued in a filing days earlier that Comey sent coded messages to his followers suggesting they kill an enemy of his citing the fictional protagonist – a federal prosecutor – in his novel FDR Drive.

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