At this point, it’s simply assumed in conservative circles that torture was responsible for the killing of Osama bin Laden. There’s ample evidence to the contrary, but for the right, the debate, such as it was, ended two weeks ago.

For those who are impervious to evidence, reality will probably never matter. But for those who still value reason, Greg Sargent has a terrific scoop today.

CIA chief Leon Panetta has written a private letter to Senator John McCain that offers the most detailed answer yet to questions about the relationship between torture and Osama Bin Laden’s death — and undercuts the claim by former Bush administration officials that torture was key to Bin Laden’s killing.

The letter has not been released publicly but was sent my way by a source. Marie Harf, a CIA spokesperson, confirmed the letter’s authenticity to me, but declined further comment.

Last week, Senator McCain published a widely discussed Op ed in the Washington Post calling into question claims that torture was instrumental in tracking down Bin Laden. McCain cited Panetta as a source for his information, but didn’t release any material provided to him by Panetta, and conservatives like former Bush attorney general Michael Mukasey subsequently dismissed McCain’s account. The CIA has not publicly taken sides in the dispute.

But Panetta’s letter, dated May 9th, bears out McCain’s version of events.

This is an important revelation. Mukasey, whose assessment was quickly embraced by the right, claimed waterboarding Khalid Sheik Mohammed produced the first grain of intelligence that got the OBL ball rolling — the name of bin Laden’s favorite courier. McCain described Mukasey’s remarks as “false.”

And Panetta’s correspondence bolster’s McCain’s judgment. Indeed, the CIA director makes clear that “no detainee in CIA custody revealed the facilitator/courier’s full true name or specific whereabouts. This information was discovered through other intelligence means.”

As Greg concluded, “In the end, we may never be able to establish with total certainty the precise nature of the relationship between torture and the killing of Bin Laden. But for now, Panetta’s account — the most extensive public accounting we now have — simply doesn’t square with claims that torture was key to getting him, which would vindicate Bush’s torture policies.”

We can only hope some of the hacks bother to read this. Fox News’ Sean Hannity, for example, told viewers a week ago, citing Panetta for support, “[W]ithout enhanced interrogation, without rendition, without black sites, this day would not have been possible. So, if we want more successful days like this, we must argue that the Obama policies were wrong and the Bush policies were right.”

This backwards assessment came a week after Obama’s policies led to bin Laden’s demise, and after McCain had already explained how wrong this line of thought is.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.