Moore said he's reviewing a previous investigation by a sheriff's office and two autopsies done on Johnson, along with photos, videos and other evidence and information. He said he's met with investigators and the attorneys for Johnson's family.
"I am committed to doing everything in my power to answer the questions that exist in this case, or as many of them as we can," Moore said.
The 17-year-old's body was found Jan. 11 stuck in an upright mat in the school gym after his parents reported him missing the night before. Lowndes County sheriff's investigators concluded Johnson died in a freak accident, but his family insists that someone must have killed him.
An attorney for the Johnsons applauded Moore for taking a closer look.
"We have to solve this murder mystery and we think the federal government's intervention is one step closer to solving this mystery," said attorney Benjamin Crump.
David S. Weinstein, a formal federal prosecutor now in private practice in Miami, said it's relatively unusual for federal authorities to go in and review an investigation once a local jurisdiction has closed it.
"There must be something in the information that was provided to him that led him to believe he needed to take another look at it," he said of Moore. "There must have been something that didn't pass the smell test."
Federal jurisdiction is relatively limited and federal authorities will only be able to open a criminal civil rights investigation if they find evidence that a law enforcement officer or someone acting as a law enforcement officer was involved in wrongdoing in the case. If they find, for example, that another person was responsible for a cover-up in the case, they would have to refer that evidence to local authorities to pursue, Weinstein said.
A southern Georgia judge on Wednesday ordered authorities to release all surveillance video that investigators reviewed. Johnson's father said after that ruling that he hoped the footage would contain clues about how he died.
Sheriff Chris Prine had previously released surveillance footage that showed Johnson entering the school gym the afternoon before his body was found. No one appeared to follow him inside.
Johnson's parents wanted to see video from the gym from the hours before their son entered until his body was discovered the next day. The sheriff had declined to release the footage without a court order because it shows other minor students who could be identified.
Johnson's body was stuck upside down in the middle of a wrestling mat that had been rolled up and propped upright behind bleachers.
The sheriff has said he suspects Johnson became trapped trying to retrieve a shoe that fell into the center of the large, rolled mat. A Georgia Bureau of Investigation medical examiner concluded that he died from positional asphyxia, meaning his body got stuck in a position in which he couldn't breathe.
Johnson's family had his body exhumed over the summer so they could get a second opinion from a private pathologist. Dr. William R. Anderson issued a report in August saying he detected hemorrhaging on the right side of Johnson's neck. He concluded the teenager died from blunt force trauma near his carotid artery and that the fatal blow appeared to be non-accidental. A lawyer for Johnson's parents filed court papers last week requesting that a judge order Lowndes County Coroner Bill Watson to hold a coroner's inquest after Watson declined the family's request to do so.
An attorney for Johnson's parents said in September that the autopsy's findings had been sent to local authorities and to Moore, as well as to the Civil Rights Division of the Justice Department.
The Georgia Bureau of Investigation has said it stands by the findings of the initial autopsy. The Justice Department said at the time that it had reviewed the state investigation file and didn't see "sufficient indication of a civil rights violation to authorize a civil rights investigation." But the Justice Department did say it was working with Moore and that his office was monitoring and evaluating the situation.
On Thursday, both of Johnson's parents said they would continue to press for answers.
"We always believed it wasn't an accident, and we still believe it wasn't an accident and we always will believe it wasn't an accident," said his father, Kenneth Johnson.
Associated Press writers Brendan Farrington in Tallahassee, Fla., and Ray Henry in Atlanta contributed to this report.