"The Viking LR experiment detected living microorganisms in the soil of Mars," Gilbert Levin flatly said.
He just happens to be the guy who invented the device to test for life on the original Viking Mars Lander back in '76. Two of the three tests proved positive, the third inconclusive- NASA therefore invalidated the entire results claiming the "false positives" were due strictly to chemical activity (something which has since been... proven false).
For arguments sake, let's say Never A Straight Answer NASA was correct- don't you then think there would be a burning scientific curiosity among them to actually do it right with further testing? Isn't that how science is done- test until proven beyond doubt? Just why is it that no NASA sponsored Mars missions since have made proving the existence of microbial life on Mars even the smallest of priorities? One of the, if not the fundamental question in the exploration of space, completely and purposely set aside by NASA. Why?