The save contains three weapon kill trophies.

Wes
Use Wes44 and kill one enemy for the trophy to appear.

MkNDI
Throw a grenade and kill one enemy for the trophy to appear. 

Dragon Sniper
There is a Dragon Sniper by the stairs. Pick it up and kill one guy for the trophy.
Here is a video if you can't find it.
http://www.youtube.com/watch?v=EnD0x2pBMMI