The mayor of Uvalde, Texas, is calling on District Attorney Christina Mitchell to resign and filed a lawsuit accusing her of repeatedly blocking the city’s investigation into last year’s shooting at Robb Elementary School that left 19 students and two teachers dead.

“It’s been fifteen months since this tragedy, and I feel the families and our community deserve answers,” Uvalde Mayor Don McLaughlin said in a written statement attached to a lawsuit filed Tuesday. Mitchell “has been involved in a cover-up regarding the City’s investigation into the Robb School tragedy,” McLaughlin alleged.

Mitchell is leading the criminal investigation into the shooting and law enforcement response, telling the San Antonio Express-News on Tuesday that she is still poring over evidence but intends to present her case to a grand jury by the end of the year.