How an obscure Oscars rule led to this year's massive best-picture screw-up

Warren Beatty was mistakenly given the wrong envelope to announce the winner for best picture at Sunday's Academy Awards in a moment that will go down as not just the biggest Oscars screw-up, but one of the biggest awards snafus ever.

But after the madness of sorting out that it was "Moonlight," not "La La Land," that won best picture, the big question was how Beatty and fellow presenter Faye Dunaway could have been given the envelope for best actress in a leading role, which went to Emma Stone, when that award had already been given out.

Beatty said onstage that the card he was given had Stone's name. Screenshots from the telecast prove he's right:

But Stone told the press room afterward that she was holding onto the best-actress envelope while she was onstage with the "La La Land" cast and producers when it was announced as best picture.

"I also was holding my 'best actress in a leading role' card that entire time. So whatever story ... I don't mean to start stuff, but whatever story that was, I had that card," Stone told reporters, in a line that quickly spawned conspiracy theories on social media. "So I'm not sure that happened. And I really wanted to talk to you guys first."

We can lay the theories to rest. It turns out that PricewaterhouseCoopers, the accounting firm in charge of vote-counting for the Oscars, shows up with two sets of envelopes announcing the winners. Employees of the firm stand on opposite sides of the stage and hand the sealed envelopes to the presenters before they go out.

So it seems Leonardo DiCaprio, who presented the Oscar for best lead actress to Stone, walked onstage from a different side than Beatty and Dunaway did, leading to the duplicate being used.

Why the need for duplicates? In an interview with MarketWatch before the Oscars, Brian Cullinan, one of the PwC accountants in charge of the envelopes, said it's to make sure Los Angeles traffic doesn't prevent getting the envelopes to the ceremony.

"We have two briefcases, that are identical, and we have two entire sets of winning envelopes. [Fellow accountant] Martha [Ruiz] carries one of those briefcases, I carry the other. We go to the show separately with police escorts. I used to think it was for our security, it's really for the briefcase. [Laughs] We take different routes to get there just because of the kinds of things that can happen in L.A. traffic. We want to make sure that no matter what happens, one of us gets there. We've never really had a problem with that."

But there are still unanswered questions, like why the PwC accountants didn't act quicker to fix the error when "La La Land" was incorrectly named the winner. It was a good couple of minutes before "La La Land" producer Jordan Horowitz stopped everything and revealed that the best-picture card said "Moonlight."

Deadline reports that one of the accountants told a stage manager about the error, and that person then went onstage with the correct card.

On Monday afternoon, The Wall Street Journal reported that Cullinan handed Beatty and Dunaway the wrong envelope. He was also tweeting from backstage. A picture he tweeted after Emma Stone won her Oscar has been deleted from his account.

PwC issued a statement late Sunday night saying it was "currently investigating how this could have happened."