The strange lights began appearing in the night sky a week before Christmas.
A formation of unidentified drones, some in groups of 30, have been reported flying high above a corner of rural northeastern Colorado and western Nebraska, usually from 7 to 10 p.m. By some accounts, the drones have wingspans of 6 feet or more.
"They can sit there and hover. They can descend very fast. They can take off very fast," Wyatt Harman, who chased the drones as they flew above his land in Washington County, Colorado, told the "TODAY" show.
He and his girlfriend, Chelsea Arnold, said they pursued the lights for about 15 miles, driving as fast as 70 mph.
"It's more unnerving than anything," Arnold said.
The couple came no closer to figuring out who or what could be behind the squadron of drones. Still, the theories abound, with some people speculating that private companies could be using the aerial robots to survey for oil or natural gas or that someone's doing practice runs for drone shows at sporting events or theme parks.
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Some have asked whether the government or the military is behind them or whether they're the work of drug cartels or are even connected to aliens.
The military has said the drones don't belong to it or come from any local bases.
In a statement, the Federal Aviation Administration said it was "in contact with local law enforcement but we don't have any concrete information to act on at this time."
The FAA announced last week that it was promoting a rule change that would require most drones to be identified remotely so law enforcement and federal agencies can ascertain who's flying them. The Denver Post reported that the proposed change has been in the works for more than a year.
For now, local sheriff's departments say the drones appear to be flying high enough that they aren't breaking any laws by trespassing on people's properties.
They're also warning people not to fire at them. Shooting down an aircraft, including a drone, is considered a federal offense.