Seven members of a Michigan militia were acquitted Tuesday of all major charges – including sedition and conspiring to use a weapon of mass destruction – after a federal judge said the prosecution failed to show the group posed a credible threat to the US government.

“The government’s case is built largely of circumstantial evidence. While this evidence could certainly lead a rational factfinder to conclude that ‘something fishy’ was going on, it does not prove beyond a reasonable doubt … [the militia members] … reached a concrete agreement to forcibly oppose” the government, wrote US District Judge Victoria Roberts.

The acquittal arrives almost two years after nine members of the Hutaree militia were arrested in Michigan, Ohio, and Indiana. FBI intelligence suggested the group was planning to kill a local police officer, then to attack the subsequent funeral procession to spark a wider militia uprising against the government.

In their raids, the agency confiscated machine guns, assault rifles, and explosive devices. An informant recorded David Stone Sr., the group’s leader, talking of plans to “go to war” against police officers and their families.

Judge Roberts said that the prosecution could not adequately determine the specifics of the group’s plans, and that it was never proven that the plot was real and not just idle talk. “The evidence of the necessary next step – a retreat to rally points from where the larger uprising would occur – is wholly lacking,” she wrote.

The judge’s decision is a lesson that speech, however disturbing, is protected, says Peter Henning, a law professor at Wayne State University in Detroit.

“The message to the FBI is, when you talk about potentially political speech, you better make sure it moved well outside of that realm and much closer to criminal conduct,” Mr. Henning says.

The trial will continue against Mr. Stone and Joshua Stone, his son, based on lesser weapons charges.

Henning says it would be misguided for groups with more sinister goals than the Hutaree to see this as a legal victory. Instead, he says, the acquittal results from the Michigan group’s clear disorganization to follow up their words with a precise plan of action.

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“Certainly the fringe groups or the militia groups are going to claim that this is some type of immunity, but that’s reading too much into this,” he says. “This was almost a gang that couldn’t shoot straight.”

Prosecutors can’t appeal Roberts’s decision because she ordered the acquittals despite the presence of a jury, which creates a double jeopardy situation that protects the defendants from the possibility of a second trial. However, the state of Michigan has the option to press separate charges.