Story highlights The Senate intelligence committee has met with Facebook officials in a closed session

Twitter officials are coming to talk to the panel Thursday in a closed session

(CNN) Sen. Mark Warner says the "million-dollar question" still unanswered about the Facebook election ads sold to Russian-linked accounts was how the Russians knew whom to target on Facebook.

Warner, the top Democrat on the Senate intelligence panel, told CNN the committee expects this week to begin viewing the 3,000 Russian-linked Facebook ads, which Facebook earlier this month disclosed were connected to more than 450 inauthentic accounts. Facebook agreed last week to turn the ads over to the House and Senate intelligence committees.

Warner's burning question involves not just the content of the ads but how they were deployed.

"Did they know this just by following political news in America? Did they geo-target both geography and by demographics in ways that at least at first blush appear pretty sophisticated? These are the kind of questions that we need to get answered and that's why we need them in a public hearing," Warner said.

The Virginia Democrat said it was "too early to tell" whether any Trump campaign officials were associated with the ads.

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