Even behind closed doors, Deputy Attorney General Rod Rosenstein won't say who told him to write the now-infamous memorandum on former FBI Director James Comey.

Rosenstein's memo, written after he learned the president intended to fire Comey and sent the next day, was cited repeatedly in the Trump administration's early explanations justifying the president's decision.

In an interview on David Axelrod's podcast published Monday, Sen. Kirsten Gillibrand, D-N.Y., revealed that Rosenstein refused to reveal who requested he write the memo during a classified briefing with senators last week. "Please clarify who asked you to write the memo," Gillibrand recalled asking Rosenstein. "And he wouldn't answer that question. … He said it could be possibly part of Mueller's probe," she said.

Of course, Gillibrand's question in and of itself presupposes that Rosenstein was asked to write the memo, ignoring the possibility he did it of his own volition. But Rosenstein's refusal to answer the question makes that scenario less likely since it would be simple and harmless enough for him to say so.

The known timeline of events is also questionable; according to the available facts, the memo did not exist until after Rosenstein was made aware of Trump's intention to fire Comey on May 8, but by Tuesday evening it had been written and sent to Attorney General Jeff Sessions and cited by President Trump in the letter he sent Comey notifying him of his dismissal.

Given the short timeline, the administration's initial decision to cling to the memo as the primary justification for Comey's firing and Rosenstein's reported refusal to answer the question, it looks a lot like Trump — or another of Rosenstein's superiors — asked him to write that memo. Considering Trump told Lester Holt he was thinking about the Russia investigation when he made the decision but that Rosenstein's memo (which did not mention the investigation) is what he cited in his letter to Comey, the story is even more questionable.

If Rosenstein approached the president with his concerns about Comey and Trump, knowing he was going to fire Comey for similar reasons, asked Rosenstein to put those concerns in writing, there would be nothing inherently wrong with that request. Furthermore, Rosenstein, for his part, may not have known the administration would use it as the primary justification for Comey's firing.

But Rosenstein's resistance to answering the question posed by Gillibrand is another indication that the most acceptable answers to key questions about Comey's firing are probably not the accurate ones.

Emily Jashinsky is a commentary writer for the Washington Examiner.