United flight 593 had to return to the Denver International Airport gate Thursday night because of three suspicious passengers on board.
According to reports, Denver Police boarded the plane after it returned to the gate and arrested four people. Everyone was taken off the plane for a security sweep.
According to the TSA, the four suspects were questioned in the terminal and were released. Witnesses described the suspects as middle aged. Two are Caucasian and two are of Middle-Eastern descent.