CHICAGO - Brendan Dassey's attorneys, in a strongly-worded motion to the U.S. Court of Appeals for the Seventh Circuit on Tuesday, urged judges to affirm a lower court ruling that overturned Dassey's conviction in the murder of Teresa Halbach.

The state's "narrative of the rape and murder of Teresa Halbach ... is spun of pure fiction," Dassey's attorneys, Laura Nirider, Steven Drizin and Robert Dvorak, wrote in the 67-page brief.

In August, U.S. Magistrate Judge William Duffin overturned Dassey's conviction, finding that the teenager's constitutional rights had been violated. The Wisconsin Department of Justice filed the initial brief in the appeal, arguing that Duffin erred in his ruling. The state's response brief, if prosecutors decide to file, is due on Dec. 21.

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In a March 1, 2006 confession, then 16-year-old Dassey adopted investigators' version of what happened to Halbach, his attorneys argued in the brief that details much of the back-and-forth between Dassey and investigators. Many parts of his confession don't make sense and it is "riddled with contradictions," they wrote.

The theme of the interrogation was that there would be no consequences if Dassey agreed with the interrogators, they wrote.

"Plainly, the officers overcame Brendan’s reluctance only by assuring him that everything would be all right as long as he confessed. But in reality, the opposite was true: because no witness or physical evidence linked Brendan to Halbach’s rape or murder, Brendan was safe from legal jeopardy unless he confessed," the post-conviction attorneys wrote in the motion.

His confession is rendered involuntary because of investigators' repeated false promises of leniency, they wrote.

"No fairminded jurist — much less any parent — can watch Brendan’s interrogation video without seeing a naïve child whose already diminished ability to make rational choices is being grotesquely distorted by false promises. The state court’s finding of voluntariness, like the confession itself, is fiction. Brendan asks this Court to affirm the district court’s grant of habeas relief."

The state court's finding that there were no promises of leniency "unreasonably overlooked facts," and the court unreasonably applied federal law in concluding that Dassey's statement was voluntary, they argued.

Dassey's attorneys also asked the Seventh Circuit "to affirm on different grounds: his conflict-ridden representation by (Dassey's former) attorney Len Kachinsky, who worked with the State to secure his conviction."

Kachinsky has previously defended his work on Dassey's case.

Alison Dirr: 920-996-7266 or adirr@gannett.com; on Twitter @AlisonDirr