LOS ANGELES — The accounting firm responsible for the integrity of the Academy Awards said Monday that its staffers did not move quickly enough to correct the biggest error in Oscars history — the mistaken announcement of the best picture winner.

PwC, formerly Price Waterhouse Coopers, wrote in a statement that several mistakes were made and two of its partners assigned to the prestigious awards show did not act quickly enough when “La La Land” was mistakenly announced as the best picture winner. Three of the film’s producers spoke before the actual winner, the coming-of-age drama “Moonlight,” was announced.

“PwC takes full responsibility for the series of mistakes and breaches of established protocols during last night’s Oscars,” PwC wrote. It said its partner, Brian Cullinan, mistakenly handed presenters Warren Beatty and Faye Dunaway an envelope containing the winner of the best actress award.

“Once the error occurred, protocols for correcting it were not followed through quickly enough by Mr. Cullinan or his partner,” the statement read.

It did not address in detail which protocols were violated, or say whether a tweet Cullinan sent about best actress winner Emma Stone before the best picture announcement contributed to the mistake.

The firm, which has handled Oscar winner announcements for eight decades, apologized to Beatty, Dunaway, the cast and crew of “La La Land” and “Moonlight,” the Academy of Motion Picture Arts and Sciences, and host Jimmy Kimmel.

The statement came after nearly a day of speculation about how the worst gaffe in Oscars history unfolded. The fiasco launched countless punch lines, memes and a probe of what went wrong.

The mystery deepened Monday afternoon after The Wall Street Journal reported that Cullinan tweeted a behind-the-scenes photo of winner Emma Stone holding her statuette. “Best Actress Emma Stone backstage!” the tweet read. The tweet, sent moments before the best picture announcement, raised the question of whether the accountant was distracted from the task at hand.

The mistaken announcement altered the usual celebration that follows the coronation of a best picture winner. The only Oscars mistake that came close occurred in 1964, when Sammy Davis was given the wrong envelope for best music score winner but made a quick correction.

The “La La Land”-”Moonlight” mix-up, in contrast, took a painfully long time to be announced, with two-plus minutes elapsing before it was announced to the moviemakers and the world at large.