A Washington, DC judge on Wednesday found a man not guilty for his alleged role in the US Capitol riot — the first acquittal tied to the Jan. 6 attacks.

Matthew Martin, a former government contractor from New Mexico, told US District Court Judge Trevor McFadden he thought police had waved him into the building and didn’t know he was breaking the law when he entered.

Based on video from the scene, McFadden said Martin’s claim was “plausible” and that prosecutors failed to prove his guilt beyond a reasonable doubt.

“People were streaming by and the officers made no attempt to stop the people,” the judge said.

McFadden, who is an appointee of President Donald Trump, found Martin not guilty after a two-day bench trial.

Martin had been charged with four misdemeanors, including disorderly and disruptive conduct in a restricted building.

During the trial, Martin claimed that he couldn’t see signs of the riot happening around him even though he shot footage of broken windows and an alarm going off when he entered the Capitol.

He said he thought an officer let him into the Capitol’s Rotunda lobby at around 3 p.m. on Jan. 6.

After viewing footage, McFadden said the officer may have given Martin that impression because he briefly interrupted people streaming into the building then stepped back to apparently allow them to enter.

“I do think the defendant reasonably believed the officers allowed him into the Capitol,” McFadden said, adding that cops were “were grossly outnumbered at that point.”

He called Martin’s conduct “about as minimal and not serious as I can imagine” among Capitol riot defendants.

Martin is the first Jan. 6 defendant to testify in his own defense.  He has reportedly called the riot “magical” and compared it to a “big block party.”

With Post wires