The wrong Best Picture winner was announced Sunday
Accountant Brian Cullinan has been named by his firm PwC as the main culprit for the "series of mistakes" that led to the biggest blunder in Oscar history.
According to a statement released by the consultancy giant, Mr Cullinan and his colleague Martha Ruiz did not follow protocols "quickly enough" once "the error occurred".
At Sunday's 89th Academy Awards, La La Land was wrongly announced as Best picture winner by presenters Warren Beatty and Faye Dunaway.
The error came to light while the La La Land team were still on the stage receiving the award, and amid chaotic scenes one of the La La Land producers walked up to the microphone and announced the real winner - Moonlight, directed by Barry Jenkins.
Breaking its silence, the Academy of Motion Picture Arts and Sciences (AMPAS) says: "We deeply regret the mistakes that were made during the presentation of the Best Picture category during last night’s Oscar ceremony.
"We apologize to the entire cast and crew of La La Land and Moonlight whose experience was profoundly altered by this error.
"We salute the tremendous grace they displayed under the circumstances. To all involved - including our presenters Warren Beatty and Faye Dunaway, the filmmakers, and our fans watching worldwide - we apologize.
"For the last 83 years, the Academy has entrusted PwC to handle the critical tabulation process, including the accurate delivery of results. PwC has taken full responsibility for the breaches of established protocols that took place during the ceremony.
"We have spent last night and today investigating the circumstances, and will determine what actions are appropriate going forward.
"We are unwaveringly committed to upholding the integrity of the Oscars and the Academy of Motion Picture Arts and Sciences."
For its part, PwC says: "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 through quickly enough by Mr Cullinan or his partner.
"We are deeply sorry for the disappointment suffered by the case and crew of 'La La Land' and 'Moonlight'. We sincerely apologise 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."
The firm has been handling the winning Academy Award envelopes for the past 83 years, adding that "last night we failed the Academy".
During the ceremony, two accountants - who are the only people to know all the winners - usually stand just off stage, monitoring the proceedings and handing out the envelopes to award announcers.
Mr Cullinan, described on the PwC website as a "Matt Damon lookalike", is the lead partner for the Academy, including the annual balloting for the awards.
He has been a part of the leadership balloting team since 2014.
He also serves as PwC’s US board chairman, and is a member of the firm's global board.
PwC says he has more than 30 years experience providing technical accounting, auditing and business advisory services to some of its largest multinational clients.