Kill all the enemies in the first part of the level, before the
elevator. Try to get all the checkpoints before the elevator.
Send the players down on the elevator, they will cross an important loading
zone. Leave one of the players waiting on the elevator.
Take the other player and find the checkpoint in the square shaped hallway.
Once it is triggered, have the player on the elevator hit the switch
to go back up.
Toss grenades when the elevator arrives at the top, just to make sure
that no checkpoints are triggered. Have both players leave the
building and go back outside.
Move fairly far away from the building (the crashed covenant ship is far
enough.) Kill both players, and hit 'start', "revert to
saved." They should respawn back underground, with one player
back on the elevator.
The player on the elevator should now see the colored corners of the
has only been found and tested on my xbox and cd.