An investigation continues into the cause of a fire that destroyed decades of archives at a social justice center that trained the Rev. Martin Luther King Jr. The Highlander Research and Education Center in Tennessee shared a press release on Facebook on Tuesday that said a symbol connected to the white power movement was spray-painted on the parking lot outside the building that burned.

"The safety of our people is and has always been our first concern. The investigation is nowhere near over," the statement said. "We are continuing to survive and monitor the process that takes more time in a rural geography with limited public resources. The Jefferson County Sheriff's Office will continue their investigation. The Tennessee Bomb and Arson people will continue to do theirs. We are not confused about how rarely people are ever charged with arson; however, we are surviving and monitoring these investigations."

Jefferson County Sheriff Jeff Coffey said Monday that investigators would remain on site for two or three more days.

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Chelsea Fuller, who is acting as a spokeswoman for Highlander, said in an email that the symbol "looks like a tic-tac-toe board" and was painted in the parking lot near the office.

"It's connected to a well-known white power movement, but they're not releasing the name at this time the local investigation is still underway," Fuller wrote.

The center has trained labor organizers and civil rights leaders including King and Rosa Parks since 1932, CBS affiliate WVLT-TV reports. Founded as the Highlander Folk School in Monteagle, it moved to New Market in 1972.

The fire early Friday destroyed one of 10 buildings located on the center's 200-acre rural property. When fire crews arrived, the building was already engulfed in flames.

Coffey declined to say whether arson is suspected.

"The fire destroyed decades of historic documents, speeches, artifacts and memorabilia from movements of all kinds including the Civil Rights Movement," according to the center's news release.