The organizers of the Conservative Political Action Conference (CPAC) have slammed Facebook’s investigation into allegations of political bias related to its Trending Topics section – saying there are still unanswered questions about the handling of stories from CPAC 2016.

The social network was thrust into the spotlight following a Gizmodo report that stories about the CPAC meeting and other conservative topics were prevented from appearing in the trending module.

CPAC, which is organized by the American Conservative Union (ACU), took place March 2 to March 5 in Washington D.C.

Facebook released the results of its probe earlier this week in a letter to Sen. John Thune, chairman of the Senate Committee on Commerce, Science and Transportation, who is investigating the allegations.

Related: Facebook denies ‘systematic’ content bias, but admits possibility of rogue employees

However, CPAC says the letter lacks sufficient detail. “Facebook appears to have conducted an investigation of itself that does not meet minimum standards of accuracy or basic explanations detailing what exactly happened with suppressed CPAC coverage,” a CPAC spokesman told FoxNews.com, via email. “They seem to admit that ‘something happened,’ but fail to explain what that was, and how and why it happened.”

In the letter, Facebook’s general counsel Colin Stretch explained how reviewers accepted topics related to both the 2015 and 2016 CPAC events. “In 2016, although topics related to CPAC were accepted on other days of the conference, one topic related to CPAC itself was not accepted on its first day, March 2, 2016,” he wrote. Facebook’s investigation concluded that this was likely due to reviewers accepting at least 15 topics related to the previous day’s Republican presidential primary.

The CPAC spokesman told FoxNews.com that the decision not to accept a CPAC-related topic on the first day of the conference is a telling one. “It confirms that coverage related to CPAC that should have been included in the ‘trending’ section was intentionally suppressed,” he said. “What was the story that was spiked, and why was it spiked?”

The spokesman also voiced his concern about Facebook’s association of Republican primary topics and CPAC. “CPAC is NOT a Republican organization - in fact, many ACU members and CPAC attendees are decidedly NOT Republicans and dislike the party,” he said.

Related: Facebook drops news outlet input in 'trending topics' review

CPAC wants more detail on why so many Republican primary stories took precedence. “The excuse for suppressing CPAC content is essentially ‘it was a heavy news day,’ the spokesman said. “ This does not provide conservatives with an explanation of what actually happened and why. It is merely speculation of what Facebook thinks probably happened.”

According to Facebook, two of the most popular CPAC stories in the news that day related to criticisms by aides to Senator Marco Rubio regarding Donald Trump’s scheduled CPAC speech and Ben Carson’s announcement that he would not attend CPAC because he was dropping out of the race. “Each of these CPAC-related stories was likely subsumed within broader topics—including Donald Trump, Marco Rubio, and Ben Carson—that were accepted by reviewers the same day,” Stretch wrote. “Given the history of acceptance of CPAC as a topic in 2015 and on most days in 2016, we do not believe any bias can be inferred.”

CPAC, however, questions how the topic of  Carson has been presented by Facebook. “Stories that ran on March 2 referred to Dr. Ben Carson not attending a GOP Debate, and announcing that he would suspend his presidential campaign at CPAC,” the spokesman told FoxNews.com. “His attending CPAC was never in question. Dr. Carson, to be sure, attended CPAC, and suspended his campaign at CPAC - what he ‘would not attend’ was a GOP Presidential debate.”

Facebook reiterated its earlier denial of any bias regarding political content in the letter to Thune. However, while the company said it found no evidence of ‘systematic’ political bias related to its Trending Topics section, the social network acknowledged the possibility that rogue employees could have impacted the controversial feature.

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CPAC told FoxNews.com that Facebook’s letter leaves conservatives with more questions, instead of answers. “We strongly urge the other individuals and conservatives who were harmed by this behavior to aggressively scrutinize the language in this document for adequate explanations and accuracy,” the spokesman said.

The firestorm over the Gizmodo report prompted Facebook to invite leading conservatives to the company’s headquarters in Menlo Park, Calif., last week to discuss the allegations. Following the meeting, Dana Perino, co-host of Fox News Channel’s “The Five,” said that Facebook recognizes that it has a “trust problem” with conservatives.

ACU Chairman Matt Schlapp declined to attend the Facebook meeting, which he described as a publicity stunt.

A spokesman for Facebook declined to add additional comment when contacted by FoxNews.com.

Follow James Rogers on Twitter @jamesjrogers