Update: Big oops. Ignore speculation below. Josh Blackman informs me that Joan Biskupic makes crystal-clear in her book that Justice Sotomayor was not a source at all.

From a Q&A with Joan Biskupic, author of a recent biography of Justice Sonia Sotomayor, I’m guessing that Sotomayor was the key leaker to Biskupic about confidential internal developments at the Court in connection with its 2013 ruling in Fisher v. University of Texas—the racial-preferences case on which the Court has again granted review.

I haven’t read Biskupic’s book, but I gather from the Q&A that her book reports that a five-justice majority was ready to strike down UT’s program of racial preferences until Sotomayor wrote “a scathing dissent that led the majority to back down.”

The large matter of ethical considerations aside, Sotomayor would be a natural suspect in any leak investigation, as Biskupic, not surprisingly, says she had a “series of conversations [with Sotomayor] in her chambers” in the midst of writing her sympathetic biography.

In what strikes me as a valiant effort to conceal her sources, Biskupic states (emphasis added):

Individual justices from both sides of the ideological divide revealed to me elements of the negotiations after what was essentially a 5–3 split against the University of Texas (Justice Elena Kagan had recused). Not all the justices would talk, and Sotomayor declined to disclose private negotiations. But I heard enough to know Sotomayor had drafted a dissent suffused with the personal experience of her Puerto Rican Bronx background.

I take the italicized sentence to signal that Sotomayor did talk with Biskupic about Fisher but merely “declined to disclose private negotiations” (on the record, at least). That leaves open that Sotomayor may well have described, or disclosed, her draft dissent and her perception of the effect that it had. It seems plausible that Biskupic then used that information to learn from—or perhaps simply to confirm with—other justices “from both sides of the ideological divide” (evidently including Justices Kennedy and Breyer) “elements” of what happened.

But perhaps I’m mistaken. Indeed, given Justice Ginsburg’s inability to keep quiet about confidential Court matters even when she is speaking publicly, perhaps she’s a strong candidate for the most likely initial leaker to Biskupic.