The concept art by Broadmore, details the length of the gun which is really helpful, but there are a LOT of inaccuracies for screen version. Don't use this for final template if you want screen-accurate. But its great for sizing.
Reference for jacket, vest, ID, and tie. Be aware that he wears TWO different outfits because the original cut of the film had evictions spanning two days. You will noticed different outfits for Wikus and Fundiswa on the latter half of evictions.
This is my best photo of the costume I made to go with the assault rifle I actually completed in time for Halloween. Cosplay is Wikus van der Merwe from the film District 9 directed by Neill Blomkamp.