Facebook co-founder Mark Zuckerberg offered an explicit apology on CNN for the misuse of personal data belonging to millions of users of the social network and talked about the steps the company will take to safeguard users’ privacy. (See the full video below.)

“This was a major breach of trust, and I’m really sorry that this happened,” he told Laurie Seiegel in an interview that aired during 360 with Anderson Cooper. “We have a basic responsibility to protect people’s data. And if we can’t do that, then we don’t deserve to have the opportunity to serve people. So our responsibility now is to make sure it never happens again.”

The CNN interview at Facebook’s Menlo Park headquarters followed an extensive response from Zuckerberg earlier in the day on Facebook, which some critics on social media said fell short of a full mea culpa. In the post, he admitted to “mistakes” and pledged to take steps to ensure “this doesn’t happen again.” Vetting thousands of apps is going to be necessary. “We have to make sure there are no more Cambridge Analyticas out there,” he said. “So we’re going to go and investigate every app that has access to a large amount of information.”

The comments marked the first public response to the Cambridge Analytica data scandal that wiped out $50 billion in market capitalization earlier this week before Facebook’s stock began to recover today.

Zuckerberg still apparently has more work to do satisfy legislators on Capitol Hill, who’ve been demanding answers in response to bombshell reports over last weekend by The New York Times and the UK’s Observer. Those investigations, which were followed by an undercover documentary on Channel 4, found that Cambridge Analytica harvested the private information from the Facebook profiles of more than 50 million users without their permission.

Asked by Siegel whether Facebook should be more tightly regulated — the scenario that has helped drive the company’s stock lower in recent days — Zuckerberg said he wasn’t opposed to it.

“I actually am not sure we shouldn’t be regulated,” he said. “The question is, what is the right regulation?” As an example of rules he supports, the exec pointed to a bill on advertising, a hot-button area given that Facebook and Google together control nearly 85% of the internet ad business. Noting the stringent rules governing ads on television, he said digital companies “should have the same level of transparency.”

Sen. Amy Klobuchar, the Minnesota Democrat who serves as the ranking member on the Judiciary Subcommittee on Antitrust, Competition Policy and Consumer Rights, turned to social media to say Zuckerberg still needs to come to Washington, D.C., to answer questions about the privacy breach.

“The steps Facebook has laid out to protect its users are a start but Zuckerberg still needs to come testify. Facebook should show good faith & support the Honest Ads Act,” Klobuchar wrote. “To truly regain the public’s trust, Facebook must make significant changes so this doesn’t happen again.”

Sen. Edward J. Markey responded to Zuckerberg’s lengthy post to deliver the same message:

Markey, who is a member of the Senate’s Commerce, Science, and Transportation Committee, earlier this week called on the committee leadership to immediately hold a hearing on Cambridge Analytica’s use of private Facebook data in its work on behalf of the 2016 Trump campaign.

Axios reports that Facebook is briefing six committees in the House and Senate on the Cambridge Analytica issue. Meanwhile, the Federal Trade Commission is reportedly examining whether the incident represents a violation of Facebook’s 2011 settlement with the agency over its privacy practices. A consent decree mandated that the social network obtain users’ permission before doing anything that “overrides” their privacy preferences.

“We take any allegations of violations of our consent decrees very seriously as we did in 2012 in a privacy case involving Google,” an FTC spokesperson said in a statement to Deadline, while declining to comment on whether an investigation is taking place.

Zuckerberg told Wired magazine that one U.K. regulator, the Information Commissioner’s Office, is conducting a probe.

“I think it might be a criminal investigation, but it’s a government investigation at a minimum,” Zuckerberg said.

The CNN interview, which didn’t exactly have razor-sharp edges, was still something different for the infamously media-shy Zuckerberg. “There’s an element of accountability where I should be out there doing more interviews. As uncomfortable as it is for me to do a TV interview, I think this is an important thing. … I should be out there being asked hard questions by journalists.”

Here’s the full CNN interview: