Idris Elba (The Wire), Sean Harris (Red Riding Trilogy), and Kate Dickie (Red Road) have joined Noomi Rapace, Michael Fassbender, and Charlize Theron in Ridley Scott's upcoming sci-fi flick Prometheus.  The Daily Mail doesn't have any details on who Elba, Harris, and Dickie will be playing, and reports that no only did the cast have to sign secrecy clauses, but "were only allowed to read the story if they visited Ridley’s production office."  As we've previously reported, Rapace and Theron will play "Elizabeth Shaw" and "Vickers", respectively, while Fassbender is playing an android.The intense secrecy surrounding the film has led to speculation that Prometheus is truly an Alien prequel despite Scott's protestations that only "keen fans will recognize strands of Alien’s DNA."  While we originally took that figuratively (the film started out as Alien prequel), the part about "Alien DNA" could be literal.  Hit the jump for more.Bleeding Cool reports that there are rumors the xenomorphs of the Alien franchise are in the movie, but you won't recognize them because they take on the appearance of their host.  BC explains:

Remember how the alien took on canine qualities after gestating in a dog? You may even suppose that the first film’s alien was so recognisably humanoid because it had grown in a human. The same applies here: generation by generation, the creature mutates. As Prometheus begins, the xenomorph is not too recognisable. Sure, it has that alien DNA that Scott and Fassbender teasingly referred to, but it’s missing… well, it’s missing human DNA. Or dog DNA.

All you have to do is imagine how it might look if it were to mix DNA with another alien species… and I think we’re starting to work it all out.

So if this is truly an Alien prequel, then the question becomes "Why hide from the Alien name?"  Do Fox and Scott believe that it's been sullied by Alien 3, Alien Resurrection, and the Alien vs. Predator films?  As Scott and the studio maintain top secrecy around the film, expect heavy rumors about the film over the year.

Prometheus is slated to open in 3D on June 3, 2012.