The head of the FBI said investigators are pushing hard to find out what happened when Michael Brown was shot and killed in Ferguson, Mo., two weeks ago, but how long it will take is unknown.

In Atlanta to meet with agents as well as local and state law enforcement officers, FBI Director James Comey touched on several topics when he spoke with reporters: racial tensions in Missouri, terrorism and public corruption.

Comey declined to discuss pending public corruption investigations ongoing in Atlanta, including one that involves DeKalb County. An FBI testifying in a government corruption trial in South Carolina said agents in Atlanta had a similar investigation into DeKalb County government on going.

He said federal investigations were “secret” for a reason, so the reputations of innocent people won’t be hurt and so the criminals won’t know they are being watched.

He also revealed little about the progress of the investigation into the fatal shooting of an unarmed 18-year-old in Ferguson, Mo., on Aug. 9

Comey said dozens of agents had been dispatched to the suburb outside of St. Louis to try to find out what actually happened when Ferguson police officer Darren Wilson fatally shot Brown.

“We care passionately about hearing all the facts,” Comey said.

He said there was no way to predict when the federal investigation would be completed and it would be up to the U.S. Department of Justice how much they will release about the FBI’s findings and how they will proceed

“The Justice Department is committed to making sure it’s (the investigation) done the right way,” Comey said.

Terrorism is a top concern for the agency, he also said. It has become even more of a threat as recruits from Western countries have joined in the fight with al-Qaeda.

“We have seen a gathering of thousands of terrorists, thousands of whom are from the West — western Europe, North American, throughout an area that is easily accessible to the United States,” Comey said. “Their going there is very worrisome because in going, they make the worst kind of relationships, they get the worst kind of training. What’s worse is the prospect of their coming back … with that training and those relationships and that awful motivation. It’s something I worry about all day, every day.”