Good modders can change the game without official documentation or backing from original developers and as of now users may have unlocked the editor for many UT3 games that are not officially supported as of yet. Mirrors Edge was first released back in the middle of November 2008, re-released on the PC two months later without any SDK or map editor to be found. Since then there has been a few maps released as DLC, which for some extended the value of the game but removed the entire premise of the game to begin with.
So the crafty tinkerers over on the Mirrors Edge community forums (unearthed by BeyondUnreal) have unlocked the secret to designing your own levels. It seems all you need is a copy of Mirrors Edge and UT3.
Beyond_Unreal wrote: To access the editor its quite easy, simply copy the wxRC and wxRes folders from your UT3\Binaries folder into your Mirror's Edge\Binaries folder and then run "MirrorsEdge.exe editor" like other UE3 based games.
Now since the discovery there have even been a few custom maps released, so this really does work. All that is left to do is create and share your maps.