After dozens of reports of drone squadrons flying in grid formations over rural areas of northeast Colorado and western Nebraska since November, state, federal and county officials joined forces to investigate. Although drones aren’t required to file flight plans, the apparent patterns and geographic coverage sparked enough interest for authorities to look into who was responsible and for what purpose.

Shortly after the new year, approximately 75 people from the Federal Aviation Administration, FBI, U.S. Air Force Office of Special Investigations, U.S. Army, Colorado Division of Homeland Security and Emergency Management, plus representatives from multiple law enforcement agencies, gathered to share information about the unidentified unmanned aerial vehicles (UAVs). Various government agencies and drone companies already denied responsibility for the drone activity, including the U.S. Department of Defense, Environmental Protection Agency and University of Colorado Boulder.

“The FAA appears to be baffled by the sightings also, stating unless a drone operator is identified, they have no recourse planned as of now,” said Yuma County Sheriff Todd Combs in a statement, reported by The Denver Post.

A task force formed at that meeting and initially focused on the possibility of a mobile command center directing the drones.

“That’s something we can handle,” Lincoln County Sheriff’s Captain Michael Yowell told the newspaper. “That’s something on the ground. A drone 500 feet in the air? We can’t do much about that. A suspicious vehicle in the middle of a county road is something we absolutely can.”

By mid-January, however, the majority of sightings were identified as planets, stars or hobby drones. Another handful were attributed to known commercial unmanned aircraft, and a few incidents remain unidentified. Furthermore, the Colorado Department of Public Safety said in a statement that they couldn’t confirm any illegal or suspicious drone activity. At that point, the department, which led the multi-agency investigation, stated it was curtailing the drone search due to lack of evidence.

“While I can’t conclusively say we have solved the mystery, we have been able to rule out a lot of the activity that was causing concern,” Stan Hilkey, Colorado Department of Public Safety executive director, said in the statement. “We will continue to remain vigilant and respond as new information comes in.”