There's a respectable contingent of scientists that believe Martian microorganisms were already confirmed 38 years ago by the Viking Lander experiments:
A future mission should definitely include a biologically-useful microscope, as suggested by USC neurobiologist Joseph Miller in the National Geograhic article linked above. Miller, also a former NASA space shuttle program director, is one of the proponents of the idea that the 1976 Viking results already demonstrated life.
The Wikipedia language suggests the existence of perchlorates (discovered in other Martian soil in 2008) could have destroyed organics during the 1976 test heating, thus explaining some of the negative results from Viking – leaving the positive 'Labeled Release' result more credible. That's the interpretation of the paper described at:
That article is currently footnote #28 of the Wikipedia article, describing the 2010 paper referenced as footnote #25. Another footnoted reference from 2011 (#29) disagrees. But presumably, all that perchlorate-related reasoning was available to the authors of the 2012 paper defending the positive result.
> However, I have the impression that, organics, in contact with perchlorates (or any strong oxidant) will result in CO2
With enough perchlorate, it will. But with smaller amounts of it, there's a huge number of possibilities, including products that are more complex than the reactants.