Michael Pena says real gangsters were used in End of Watch
22 November 2012 Last updated at 06:14 GMT
Actor Michael Pena says that working on his new film End of Watch was a "scary" experience due to the use of real gangsters in certain scenes.
Pena plays a Los Angeles police officer in the movie and admits that it took more than five months of training to prepare for the role.
The film also stars Jake Gyllenhaal and has been talked about as a potential awards contender.
The actor was speaking to Newsbeat's entertainment reporter Nesta McGregor.
End of Watch is released in the UK on 23 November.