In the radio interview, McCulloch also defended the decision to make the announcement at night, saying it was best for schools and allowed business owners time to decide whether to open the next day.
State Rep. Karla May is pushing for a state investigation of McCulloch and whether he "manipulated" the grand jury into the decision.
A joint House and Senate committee is already investigating why Gov. Jay Nixon did not use National Guard troops in Ferguson on Nov. 24. May, a St. Louis Democrat, sent a letter Thursday to committee chairman Sen. Kurt Schaefer, urging that the investigation expand to look at whether McCulloch committed prosecutorial misconduct.
"Many St. Louis-area residents believe — and there is at least some evidence to suggest — that Mr. McCulloch manipulated the grand jury process from the beginning to ensure that Officer Wilson would not be indicted," May wrote.
She said in an interview that McCulloch should have removed himself from the case at the outset.
"I don't believe he followed proper procedures when he presented evidence to the grand jury," May said. "To me, he was working for the defendant in this case and not the victim."
Critics had called for McCulloch to either step aside or for Nixon to appoint a special prosecutor, citing concerns about whether McCulloch could fairly oversee the case. McCulloch's father was a police officer killed in the line of duty by a black assailant in the 1960s.
McCulloch said immediately after the announcement that the jury of nine whites and three blacks met on 25 separate days over three months, hearing more than 70 hours of testimony from about 60 witnesses, including three medical examiners and experts on blood, toxicology and firearms and other issues. He said he assigned prosecutors in his office to present evidence, rather than himself, because he was "fully aware of unfounded but growing concern that the investigation might not be fair."
Ferguson Mayor James Knowles III and others expressed anger that of the hundreds of National Guard troops dispatched to the St. Louis region on Nov. 24, none were in Ferguson as the announcement was made.
No timetable has been set for the legislative committee's investigation, and it wasn't clear if the committee would consider investigating McCulloch. A message left with Schaefer was not immediately returned.
The Associated Press