Gil Levin, one of the scientists involved with the 1976 Viking mission to Mars, has claimed and continues to claim that there is life on Mars, based off the positive results of the Labeled Release (LR) experiment.
This was the only one of the landers' four life-detecting instruments that returned positive results, but prior to the mission it was expected that because of the instruments' radically different approaches, actual Martian organisms might still only return positive results in one of them. Furthermore, there is no evidence (to my knowledge) that the LR instrument was faulty, nor that LR's strong positive results could be explained by any non-biological process. (Levin details his fairly comprehensive explanation and argument for life on Mars in this paper).
Despite these findings, scientific consensus still posits that no life on Mars has ever been detected, by LR or any other experiment. My question is simply: Why?
Can anyone point me to a credible source, statement, or publication that addresses LR's results and explains why they don't constitute sufficient evidence for life on Mars?