Early this year, the journal Nature published two papers with some completely surprising results. Researchers had only recently figured out how to use a small set of genes to reprogram mature adult cells into a stem-cell-like state. The new papers suggested you could forgo the genetic engineering entirely; a short time in an acidic environment, followed by some carefully controlled growth conditions, could completely reprogram the cells. It was a potentially revolutionary finding.

Unfortunately, it didn't take long for the wheels to fall off. Other researchers quickly pointed out possible instances of improperly manipulated figures and plagiarism, and one of the researchers involved had already had some ethical issues in the past. Initial attempts to replicate the experiments in other labs failed. By the summer, there was an official finding of misconduct; shortly thereafter, one of the researchers involved committed suicide. In July, the papers were formally retracted by the remaining authors.

That's a relatively quick resolution to a problem like this, but it leaves a rather significant question: how did these papers get published in the first place if the problems became apparent so quickly? That question only got more bewildering this week, as people have started to leak the reports of peer reviewers who had evaluated the papers.

The first leak was published yesterday by the Retraction Watch blog. It turns out that Nature was the third journal to see the drafts of the stem cell papers; by the time it got them, Science and Cell had already rejected them. Someone who had access to the reviewers' reports at Science handed them over to Retraction Watch.

The reviews are pretty negative. Two of them suggest that the results could easily be an artifact; one lists over 20 issues with the paper as written, while another says that the experimental detail is far too vague. The editors at Science accepted the judgement of the reviewers and rejected the paper. Which, to an extent, suggests that the paper must have gotten better reviews at Nature.

But that idea got put to rest Thursday, as someone leaked the reports from the reviewers that Nature had used. And they identify most of the same issues that the earlier reviewers had spotted—along with a host of new ones. Again, a lack of details on the experiments and the possibility that the authors didn't conclusively demonstrate what they claimed featured prominently. Nature rejected the paper as it stood, but offered to reconsider it if the authors could address the problems that the reviewers had identified.

This happened in April of 2013. Sometime between there and January of 2014, the papers were accepted. Presumably they underwent considerable revision, but some of the problems—most notably the lack of details about how the work was actually done—clearly remained. The mystery of how this suddenly became acceptable for publication has yet to be solved.