But after what seems an exhaustive review of a now voluminous record of transcripts, exhibits and other evidence from multiple official inquiries, Professor Ball concludes there is “no evidence” that the decision-makers “examined the adequacy of Lehman’s collateral, or that legal barriers deterred them from assisting the firm.”

Rather, the decision to let Lehman fail reflected a mixture of politics — Mr. Paulson famously said he didn’t want to go down in history as “Mr. Bailout,” and the Bush administration had come under fierce criticism for rescuing Bear Stearns and the mortgage giants Fannie Mae and Freddie Mac — economic policy driven by managing “moral hazard,” and a misguided sense that investors had anticipated a Lehman failure and the consequences would be manageable.

“It’s out of the mainstream of what most academics do,” David Romer, a professor of economics at the University of California, Berkeley, told me this week about Professor Ball’s paper. (Professor Romer read and commented on an early draft.) “It’s likely to offend some people and be controversial. But with respect to the specific questions he asks” — did the Fed have the legal authority to lend and was it forced to shut Lehman down — “I find his answers pretty compelling.”

Professor Ball has an impressive roster of mainstream economics credentials: He has a Ph.D. in economics from the Massachusetts Institute of Technology, taught at Harvard and Princeton, is a visiting scholar at the International Monetary Fund and is a research associate at the National Bureau of Economic Research.

“Larry Ball’s carefully researched work is incredibly important for drawing the proper lessons from the 2008 crisis,” said Athanasios Orphanides, an economics professor and expert on central banking at M.I.T.’s Sloan School of Management.

I did speak to several people who remain unpersuaded (none willing to be identified), and it’s fair to say no one paper will ever fully resolve this debate. Several said that, however impressive in the abstract, Professor Ball’s analysis was missing a real-world perspective, which was that almost no one believed at the time that Lehman was solvent and virtually nothing short of a politically untenable federal takeover of Lehman would have staved off a run. Defenders of the theory that Lehman was deeply insolvent also point to the fact that Lehman’s creditors ended up suffering tens of billions of dollars of losses in the bankruptcy.

None of the principals themselves have budged from their oft-stated positions that the Fed’s hands were tied. Mr. Paulson said he stood by earlier comments he gave me: “We were united in our determination to do all we can to prevent a systemically important institution from going down.” He added, “Although it was Ben and Tim’s decision to make, I shared their view that Lehman was insolvent and I know the marketplace did.”