Brian Cullinan, one of the two PriceWaterhouseCoopers partners who handled the Oscar envelopes on Sunday night, was tweeting photos from backstage minutes before he handed Warren Beatty the wrong Best Picture envelope.

PricewaterhouseCooper is taking the blame for a fiasco that saw “La La Land” mistakenly named Best Picture at Sunday’s Academy Awards. The accounting firm has tabulated Oscars voters’ ballots since 1934. Cullinan has worked on the Oscars for four years. He handed presenters the wrong envelope, one that had the name of best actress winner Emma Stone instead of the producers of “Moonlight,” the film that ultimately took the top honor.

It turns out that the mistake may have been made because Cullinan, a managing partner at the firm and one of the accountants tasked with making sure the right names get read out on Oscar night, was busy tweeting about the show instead of carefully overseeing the envelopes, according to two knowledgeable insiders. Cullinan had been congratulating winners throughout the evening. After the wrong Best Picture winner was announced, he deleted the tweets from his Twitter account. Screengrabs reveal that Cullinan tweeted four times during the broadcast, at one point talking about the red carpet and the build-up to the broadcast, and in another instance lauding Viola Davis for her Best Supporting Actress victory speech. Three minutes before the fateful hand-off, Cullinan took a photo of Emma Stone clasping the gold statue she picked up for “La La Land.”

PWC’s Brian Cullinan later deleted this tweet of Emma Stone backstage. Twitter

“Best Actress Emma Stone backstage! #PWC,” Cullinan tweeted. Moments later, Beatty, who was presenting Best Picture, looked visibly puzzled as he opened the envelope, handing it to co-presenter Faye Dunaway to make sense of things. She then mistakenly read out “La La Land’s” name as the evening’s winner.

In an earlier interview, Tim Ryan, U.S. chairman and senior partner of PWC, told Variety that Cullinan pulled from the wrong pile. He had a pile of envelopes for people entering from one side of the stage, while Martha Ruiz, another PwC partner, oversaw a separate pile for people entering from his side of the stage. Ryan said Cullinan simply pulled from wrong pile.

Ryan said he had spoken to Cullinan about the episode at length. “He feels very, very terrible and horrible. He is very upset about this mistake. And it is also my mistake, our mistake, and we all feel very bad,” Ryan said.

A spokesperson for PwC did not respond to a request for comment on Cullinan’s tweeting. The company did tweet an apology Monday night:

“PwC takes full responsibility for the series of mistakes and breaches of established protocols during last night’s Oscars. PwC partner Brian Cullinan mistakenly handed the back-up envelope for Actress in a Leading Role instead of the envelope for Best Picture to presenters Warren Beatty and Faye Dunaway. Once the error occurred, protocols for correcting it were not followed quickly enough by Mr. Cullinan or his partner.

We are deeply sorry for the disappointment suffered by the cast and crew of ‘La La Land’ and ‘Moonlight.’ We sincerely apologize to Warren Beatty, Faye Dunaway, Jimmy Kimmel, ABC and the Academy, none of whom was at fault for last night’s errors. We wish to extend our deepest gratitude to each of them for the graciousness they displayed during such a difficult moment.

For the past 83 years, the Academy has entrusted PwC with the integrity of the awards process during the ceremony, and last night we failed the Academy.”

James Rainey contributed to this report.