McCulloch, who has held the office since 1991, insists he’ll conduct a fair, evenhanded investigation. “I appreciate and understand the concerns of those who honestly believe that I cannot or will not be fair to all in the gathering and presentation of the evidence pertaining to the tragic death of Michael Brown,” he wrote in a statement released Thursday. “Although I understand the concerns, and do not take lightly the demands that I recuse myself from this case, I also recognize that I have a responsibility to the family of Michael Brown, the people of Ferguson and the entire community.”

But supporters of the Brown family are skeptical, pointing to McCulloch’s personal and professional history.

To start, he has a close familial connection to violence. In 1964 his father—a police officer—was shot and killed by a Black man in a public housing complex, which critics say affects his judgment of police brutality cases. In particular, they point to a case in which McCulloch declined to bring charges against two detectives accused of excessive force in the killing of two unarmed Black men.

“McCulloch’s decision not to charge officers who murdered two unarmed African-American men in 2000 by shooting into their car 20 times,” writes state Sen. Jamilah Nasheed in a letter attached to the petition, “gives us no confidence that his office can provide a fair and impartial investigation into this current matter.”

Recent comments from McCulloch add fire to the criticism. Last Thursday he blasted Nixon for replacing St. Louis County police control of the Ferguson protests with officers and leadership from the Missouri State Highway Patrol. “It’s shameful what he did today, he had no legal authority to do that,” McCulloch said. “To denigrate the men and women of the county police department is shameful.”