AUSTELL, Ga.—A teenager was decapitated by a roller coaster after he hopped a pair of fences and entered a restricted area Saturday at Six Flags Over Georgia, authorities said.

Six Flags officials are uncertain why the unidentified 17-year-old from Columbia, S.C. scaled two six-foot fences and passed signs that said the restricted area was both off-limits and dangerous to visitors, spokeswoman Hela Sheth said in a news release.

Authorities were investigating reports from witnesses who said the teenager jumped the fences to retrieve a hat he lost while riding the Batman roller coaster, said Cobb County police Sgt. Dana Pierce. Police have declined to release the teenager’s name until an autopsy is completed.

Six Flags said it closed the roller coaster after the Saturday afternoon accident out of respect for the teen’s family. The ride was expected to reopen on Sunday, according to a Six Flags news release.

Police said the ride was going full-speed when the teen was struck. The ride’s top speed is 50 mph, according to the park’s Web site.

No one riding on the roller coaster was injured, Sheth said. The teen was with another boy who also entered the restricted area but was not injured, Pierce said.

The teen and his parents were at the park with a group from the Oakey Spring Baptist Church near Springfield, S.C., police said.