CHEYENNE, Wyo. (AP) — People insist they have spotted fleets of large drones crisscrossing rural America’s night sky, their mission mysterious, raising questions that have veered into conspiracy theories and launching an investigation.

Authorities in Colorado have tried to put those theories to rest, announcing that they have confirmed nothing unusual or criminal about dozens of weird drone reports since November. They were mostly hobbyist drones, commercial aircraft, stars, planets and weather phenomena.

Yet if history is any guide, the investigation that used a heat-detecting plane in Colorado’s mystery-drone highway, with sightings that stretched into Nebraska and Wyoming, will settle nothing for many people.

Speculation persists about drones said to be as big as cars, flying in groups in grid patterns at night.

“Even if the military has plausible deniability with this, defense contractors might be involved,” Dan Carlson, a drone-spotting retired meteorologist in western Nebraska, said Tuesday. “By the time they ’fess up to it, they’ll have been in sky for four years.”

Four times this year, Carlson said, drones have flown after dark near his farm outside Sidney, Nebraska.

Drones flew in pairs on two nights, he said. Their speed, impressive range — over the distant horizon without landing — and proximity to nearby missile silos makes him suspect the U.S. Air Force at least knows of the flights.

Uncertainty, if not paranoia, has proliferated about such sightings. Just don’t count Carlson among those peddling out-of-this-world explanations.

“I do not buy into the conspiracy theories. I am not living in fear of an alien invasion,” he said.

He speculates the drones may be involved in some kind of military search-and-recovery practice, pursuing items hidden around the countryside during the daytime for training exercises at night.

F.E. Warren Air Force base in Cheyenne, Wyoming, oversees 150 Minuteman III nuclear missiles in silos scattered across the prairie in the three-state region. The missiles need regular checking, maintenance and protection against threats, yet Air Force officials insist the drone reports have nothing to do with them.

“Our base is kind of a drone no-fly zone. So we do have counter-UAS — unmanned aerial systems — training that goes on within the confines of this installation. But any drones spotted outside this installation are not part of our fleet,” said Lt. Jon Carkhuff, a base spokesman.