Democratic Gov. Jay Nixon said Sunday St. Louis County Prosecutor Bob McCulloch should “step up” his investigation into the fatal police shooting of Michael Brown last weekend in Ferguson.

“I think it’s a time [for] the local prosecutor to have the opportunity to step up. I know everybody’s working really hard. It’s important we get this right. This is a big matter,” Nixon told CNN’s State of the Union. “Clearly, the death of an 18-year-old at the hands of a law enforcement gun is something that’s caught a nerve, not just here in Missouri, but across the nation and the world.”

Nixon said the parallel investigation launched last week by by the U.S. Department of Justice – boosted this weekend by the deployment of 40 additional FBI agents into the area – could help solidify information in the case more quickly.

“I’m confident the Justice Department will, with the additional resources and focus here, that General Holder and the FBI and folks are going to get the information and get it to the proper choosing authorities, in my sense, in a timely fashion,” he said.

McCullouch’s objectivity in the matter has been questioned by local political leaders, including State Sen. Jamilah Nasheed, a fellow Democrat. She launched an online petition earlier this week calling for him to be replaced by a special prosector to investigate the police shooting citing his decision to “not to charge officers who murdered two unarmed African American men in 2000 by shooting into their car 20 times.” The petition has garnered more than 21,000 signatures.

When asked specifically about criticism of McCullouch, Nixon told CNN: “He’s an experienced prosecutor. And this is his opportunity to step up.”

“Everybody understands and he’s said in public that they’re going to present evidence to a grand jury,” Nixon added. “I think that the dual, parallel investigations of Justice and the local really, really add both a – they just help.”