(CNN) Colorado investigators say they found no incidents of criminal activity following an investigation into mysterious drone sightings over Colorado and Nebraska.

"In response to public concern over reports of unusually large-sized drones flying patterns in groups, (the Colorado Department of Public Safety) has been gathering and analyzing information since November 23 and has conducted field investigations since January 6," CDPS said in a news release

But their investigations didn't substantiate the drone reports, the release said.

The department said Colorado officials had received 90 reports of drone activity between November 23 to January 23 and of those, 14 were confirmed to be hobbyist drones.

It also said that there were 23 drone reports since January 6 -- 13 of which were determined to be "planets, stars or small hobbyist drones," six were ruled out as atmospheric conditions or commercial aircraft and the last four couldn't be identified by law enforcement.

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