Facebook is launching a new investigation into whether Russian propagandists coordinated a disinformation campaign around the 2016 Brexit vote. In a letter to the head of a parliamentary committee on digital affairs, UK policy director Simon Milner says Facebook will conduct “detailed analysis of historic data” over a period of several weeks. It’s looking for accounts that it may have missed in a December probe, which found little evidence of potential Russian interference — a conclusion that the committee head, MP Damian Collins, disputed.

Milner writes that the earlier investigation focused on the Internet Research Agency, a Kremlin-linked company that’s allegedly behind many US-based fake accounts. In response to Collins’ request for closer investigation, Facebook “can confirm that our investigatory team is now looking to see if we can identify other similar clusters engaged in coordinated activity around the Brexit referendum that was not identified previously.” Milner also requested any information, “including intelligence assessments or reports,” that might help the new hunt.

Facebook said in November that it had not seen “significant coordination” to sway the Brexit vote, shortly after defending itself to the US Congress. But the company hasn’t ruled out possible meddling. The new probe may offer more details about the scope of Russia-linked propaganda accounts — and relieve political pressure on Facebook in the UK.

Correction: The Brexit vote was in 2016, not last year.