A manager who worked on privacy issues at Facebook told FRONTLINE that he raised red flags to company executives more than five years ago about the risks that users’ personal data could be inappropriately obtained and misused, but said his warnings went unheeded.

Sandy Parakilas was a platform operations manager at Facebook between 2011 and 2012. After news broke last weekend that a political data firm that worked on Donald Trump’s presidential campaign had harvested information from Facebook users, Parakilas told The Guardian that Facebook had not moved strongly enough to safeguard the privacy of users.

Last month, Parakilas told the story of his concerns to FRONTLINE in his first in-depth television interview about his time at Facebook. The interview, part of an ongoing investigation by FRONTLINE into the influence of social media platforms, was conducted before the new reporting that the firm Cambridge Analytica had obtained personal information from millions of Facebook users by exploiting a Facebook policy governing app developers.

In the video above, Parakilas said he had warned that outsiders could game Facebook rules to collect personal information on users. While Facebook policies were later changed, Parakilas said that at the time, his concerns were not taken seriously.

“I became more and more concerned about the broader data infrastructure of Facebook and the amount of data that Facebook had about its users and the vulnerabilities that the system had,” he said. “And so I started thinking through what are the worst case scenarios of what people could do with this data?”

Parakilas said he shared his concerns with senior executives, “among the top five executives in the company.”

A Facebook spokesman did not respond directly to Parakilas’ account, but referred FRONTLINE to a statement by Paul Grewal, the company’s deputy general counsel, saying, “We are in the process of conducting a comprehensive internal and external review as we work to determine the accuracy of the claims that the Facebook data in question still exists. That is where our focus lies as we remain committed to vigorously enforcing our policies to protect people’s information.”

The spokesman also pointed to a blog post last November from a Facebook executive describing a series of measures taken by the company to strengthen its privacy protections. While Facebook had always guarded against misuse of data, the post said, “in the past five years we’ve significantly improved our ability to detect and prevent these violations.”

Cambridge Analytica has denied improperly obtaining or misusing information about Facebook users.