When angels sinned, God did not let them go free without punishment. He sent them to hell and put them in caves of darkness where they are being held for judgment.
And remember the angels who did not keep their place of power but left their proper home. The Lord has kept these angels in darkness, bound with everlasting chains, to be judged on the great day.
Then I saw another powerful angel coming down from heaven dressed in a cloud with a rainbow over his head. His face was like the sun, and his legs were like pillars of fire.
Then he threw him into the bottomless pit, closed it, and locked it over him. The angel did this so he could not trick the people of the earth anymore until the thousand years were ended. After a thousand years he must be set free for a short time.