What really happened?

A week from Tuesday will be the second anniversary of Lehman Brothers’ bankruptcy and the ensuing panic that helped spawn the deepest recession since the Great Depression. Yet two years on, a mystery remains about the fateful weekend before Lehman’s fall.

Last week, during the Financial Crisis Inquiry Commission’s final hearings, entitled “Too Big to Fail,” two competing versions of events were revisited about the last frantic 72 hours of Lehman’s life: That the government did not have the legal “authority” to rescue the firm or, more conspiratorially, that the firm was knowingly killed because politics made it impossible to save.

A trove of new e-mails and notes released as part of the...