Originally Posted by Hyakotake
i got it after saving barney on the rooftop, but i remember killing two snipers in an earlier level... i distinctly remember there is a sniper when youre going along a train track, and he is sitting in a closed walkway above the tracks... so do these two early snipers count too?
No, only the five on "Follow Freeman!" count.
I just got the Conservationist achievement on the level "Dark Energy". I waited until Breen was in his bubble, then ran up to where there are three columns of energy balls. When you approach the first one, three enemies come out. If you suck the three balls out of it and proceed to the second one, another three enemies come out (six in total). It's then just a case of grabbing an energy ball from the column, heading back to where they are, waiting until they are reasonably lined up and firing.
Might take a few tries but that's what worked for me.