A light that appeared high over St Louis's Gateway Arch is perplexing officials.
The mystery started when an Illinois man shot video of the light and shared it with KTVI-TV.
After seeing the report, an employee at an Illinois park across the river from the arch took a look at footage from a security camera and saw the same light.
The video has been posted on the park's Facebook page.
Mike Buehlhorn, director of the Metro East Parks and Recreation District, said he does not know if he believes in UFOs, but "there's something weird with that one".
Spokesmen for nearby Scott Air Force Base and the Federal Aviation Administration said they know nothing about the source of the light.