re: More organics found by Mars Express???
On earth you could compare the isotopic ratios of the carbon, since life prefers C14, or maybe the other way around, but in any case there is a difference in isotopes between biogenic and non-biogenic products.
-- is it feasible to miniaturize the equipment needed to measure isotope ratios for something like a rover?
-- is there any reason to expect Mars organisms to show the same bias?
I defer to anyone who knows what they are talking about to answer those questions....