The Teselecta is one of the most remarkable pieces of engineering the Doctor has ever encountered. A vehicle that can be shape-shifted into any form, it’s operated by a miniaturized crew of 421, maintained in that state by a compression field. The Teselecta the Doctor encountered in Berlin, 1938, was Justice Department Vehicle 6018.
Traveling through history on behalf of the Justice Department, and replacing major criminals seconds before their death, they take the originals away for whatever punishment they think is appropriate. They contain incredibly in-depth records of everyone throughout history as well as Anti-Bodies, robotic assassins that erase the real criminals once they are brought aboard. Only the crew are safe from the Anti-Bodies provided they wear special wristbands that identify them as non-hostile.