A federal appeals court on Thursday sent back a lower court's order for a suburban Atlanta school district to remove textbook stickers calling evolution "a theory, not a fact," citing a lack of evidence in the case.

The 11th U.S. Circuit Court of Appeals said the federal district court must determine whether the government's actions are "religiously neutral." The ruling by the three-judge panel means the case could be retried.

"We simply choose not to attempt to decide this case based on a less-than-complete record on appeal or fewer than all facts," the panel wrote.

The Cobb County school system was ordered in January 2005 to remove the stickers from the inside front cover of 35,000 biology textbooks after a U.S. District Court judge ruled they represented an unconstitutional endorsement of religion. To comply, school staff and students scraped the stickers from all the books months later.

It had been the school's policy since 1995 to tear out chapters on evolution from science textbooks out of "respect for the family teachings of a significant number of Cobb County citizens," according to Thursday's opinion. But, in the spring of 2002, when the school district selected a new biology book that contained 101 pages on evolution, school officials decided to affix a disclaimer sticker instead of removing the section.

Parents of some students sued, claiming that the stickers violated the First Amendment clause that separates church and state. The district court judge ruled in their favor, saying the argument that evolution is a theory and not a fact is a distinction made by religiously motivated individuals.

"The school's position is that the sticker wasn't there in violation" of the First Amendment, Cobb County schools attorney Glenn Brock said Thursday. "It was there to promote critical thinking."

At the heart of the federal appeals court ruling is whether school officials had been pressured into adopting the stickers. The lower court said school officials responded to a 2,300-signature petition that demanded the disclaimer, but the appeals court panel was never presented a copy of the petition or evidence that one was ever submitted before the school system opted for the stickers.

A telephone message left at the office of Michael Manely, one of the parents' attorneys, wasn't immediately returned Thursday.