Though DICE regularly makes use of its internally-developed technology, the Mirror's Edge project began early in the development of its Frostbite engine, prompting the studio to use Epic's technology instead.
"With Mirror's Edge we deliberately set out to create something that was different from Battlefield," said a studio representative. "Frostbite is a very powerful engine but this project started a long time ago, and at that time Frostbite was still being developed and was very closely supporting the Battlefield Bad Company team."
Epic's Unreal Engine 3 has been licensed for use in development by a number of studios including Konami, 2K Games, and John Romero's Slipgate Ironworks studio. For more on Mirror's Edge, be sure to check out the new trailer.