A former Justice Department employee who threw a sandwich at a federal agent during US President Donald Trump’s law enforcement surge in Washington was found not guilty of assault on Thursday in the latest legal rebuke of the federal intervention.

A viral video of the sandwich tossing made Sean Charles Dunn a symbol of resistance to Trump’s deployment of federal agents to combat crime in the nation’s capital.

His misdemeanour acquittal is another setback for prosecutors, who have faced a backlash for their aggressive charging tactics during the law enforcement surge.

The Justice Department had initially sought a felony assault indictment against Dunn, but in a highly unusual move, the grand jury declined to sign off on the felony charge. The office of US Attorney Jeanine Pirro then charged Dunn with a misdemeanour.

There was no dispute over whether Dunn threw the sandwich at a US Customs and Border Protection agent on the night of August 10. But his lawyers argued it was a “harmless gesture” during an act of protest protected by the First Amendment.

Prosecutors said Dunn knew he did not have a right to throw the sandwich at the agent.