Law enforcement and fire officials were investigating a potential threat on a plane at Denver International Airport, but police later said the threat was unfounded.

A Frontier Airlines flight from Seattle was evacuated at Denver International Airport on Monday after crewmembers discovered two threatening notes on board, but police later determined the threat was not credible. Flight 3406 landed safely at DIA around 11:15 a.m., about an hour behind schedule.

A plane was given the “all clear” Monday after threatening messages were found on board mid-flight.Frontier Flight 3406 left Seattle Monday morning, bound for Denver International Airport. The airline says that at some point during the journey,