St. Paul City Council Member Dai Thao didn’t know he was breaking the law when he helped a woman vote while he was running for mayor last fall, and election judges at the polling place did nothing to stop him, according to a motion Thao’s attorney filed Friday.

In a 21-page motion brief filed in Ramsey County District Court, attorney Joe Dixon argued that prosecutors have failed to prove that Thao knowingly broke the law and that the case against him violates federal law and the U.S. Constitution.

“Based on the undisputed facts, and given the State’s own acknowledged complicity, the State’s prosecution of Mr. Thao is not only unconstitutional and legally deficient, it is patently unfair,” Dixon wrote.

The motion asks for the case to be dismissed or for Thao to be found not guilty. The 42-year-old council member faces three misdemeanor counts of unlawfully marking a ballot, misconduct in and near polling places and unlawfully assisting a voter. Minnesota law prohibits candidates for office from assisting voters.

According to the motion, on Nov. 6, while Thao was running for mayor of St. Paul, he drove a 63-year-old Hmong woman who did not speak English to an early voting site and interpreted for her and for election judges as he helped her register to vote. The woman, who could not see well, asked Thao to help her vote, and he did.

“Election judges knew who Dai Thao was and that he was a candidate,” the motion said. “Even so, the election judges said nothing and made no effort to stop Mr. Thao from assisting the elderly woman — until after she had voted.”

When an election judge told Thao that he couldn’t assist voters, Thao responded, “Oh, I didn’t know,” and explained that the woman had asked for his help, according to the motion. Thao had helped people vote before he was a council member, the motion said, and the state campaign manual he was provided did not say that candidates are prohibited from assisting voters.

The motion also argued that Thao’s conduct is protected by the federal Voting Rights Act, which allows voters to choose anyone to help them vote.

A pretrial hearing is scheduled for Aug. 13.