We know its not Tool (Mickey Rourke). He is not appearing in the film and murdering him off screen holds no weight whatsoever. I believe the following photo MAY hold a clue to the answer.
So we must ask ourselves now...does the death of Gunnar Jensen pack weight? Possibly...he was almost killed in the first film and maybe does actually bite the dust this time around. But I think the death that would really pack some weight....that would really eat away at Barney Ross (Sylvester Stallone)....would be the death of Lee Christmas.
The answer to this question may come in the next trailer with scenes of the murder shown but I doubt it. If they didn't reveal the name in the plot summary I'm guessing they want it to be a surprise. My guess at the end of the day is we will see the murder of Lee Christmas. This not only provides the reason for Barney's depressed display in the trailer but provides the opportunity for the introduction of a new major team member for a proposed Expendables 3. Who knows? I could be completely wrong on this but only time will tell.
What do you guys think?