Facebook's outgoing head of communications is taking the blame for hiring Definers, the public relations firm doing opposition research on the company's critics, including billionaire philanthropist George Soros.

In a Facebook post that went up late Wednesday, Elliot Schrage said the responsibility to hire Definers rests with him and that he approved the decision to hire it and similar firms.

Schrage provided his explanation in a message sent Tuesday to Facebook's employees, but the company waited until late Wednesday to publicly share it at a time when most people in its home country were focusing on the Thanksgiving holiday weekend. Facebook CEO Mark Zuckerberg also didn't mention Schrage's role in hiring and working with Definers in an interview with CNN aired late Tuesday.

Definers' link to the Menlo Park, Calif., company was exposed in a story published by the New York Times earlier this month.

Schrage has been at Facebook for a decade and announced his departure in June. In the post, Schrage acknowledged that Facebook asked Definers "to do work" on Soros after he called Facebook a "menace to society" in a January speech. Definers also helped respond to what Schrage described as unfair claims about the company.

"We had not heard such criticism from him before and wanted to determine if he had any financial motivation," said Schrage.

I did not know we hired them or about the work they were doing, but I should have. I have great respect for George Soros — and the anti-Semitic conspiracy theories against him are abhorrent. - Sheryl Sandberg, Facebook COO

Even so, Schrage conceded that Definers' got carried away in its work to discredit Facebook's critics. The system he set up on the company's communications team "failed here, and I'm sorry I let you all down," he wrote.

Sheryl Sandberg, Facebook's chief operating officer, followed Schrage's note of contrition with one of her own, acknowledging her responsibility for overseeing Facebook's communications team. Like Schrage, Sandberg was a top executive at Google before coming to Facebook a decade ago.

"Some of their work was incorporated into materials presented to me, and I received a small number of emails where Definers was referenced," Sandberg wrote.

The Times report said the research activities, which included members of U.S. Congress, ramped up as Sandberg prepared to testify this past summer at a Senate intelligence committee hearing that addressed how Russian actors and others used the social media giant to sow discord during the 2016 U.S. presidential election campaign with fake accounts and divisive posts.

Cut ties with PR firm

Zuckerberg, who is Facebook's controlling shareholder as well as its CEO, is standing behind Sandberg, despite the backlash caused by the company's retention of Definers and its campaign against Soros. He told CNN on Tuesday that he hopes to work with Sandberg "for decades" to come.

As for the work of Definers, Zuckerberg told reporters last week, "I understand that a lot of D.C.-type firms might do this kind of work. When I learned about it I decided that we don't want to be doing it."

Schrage said the company worked with PR firms that were associated with both major U.S. parties, though he admitted Definers was "one of the Republican-affiliated firms."

Hard-right conservatives have frequently tried to tie Soros, 88, to issues they are opposed to — most recently, accusations he's helped fund the Central American migrant caravan and the bid to thwart Brett Kavanaugh's nomination to the Supreme Court. Conspiracy theories have also led to Soros, born in Hungary to Jewish parents, being accused of being a Holocaust sympathizer; Roseanne Barr tweeted one such accusation during the storm of social media posts in May that saw her eventually fired from her hit television show.

Soros's Connecticut home is believed to be the first known site to receive recent pipe bomb mailings targeting Democratic politicians and liberal figures.

Facebook stopped working with Definers after the New York Times investigation unveiled its tactics.

"I did not know we hired them or about the work they were doing, but I should have," said Sandberg. "I have great respect for George Soros — and the anti-Semitic conspiracy theories against him are abhorrent."