A former Cambridge Analytica executive is cooperating with Special Counsel Robert Mueller’s investigation into collusion between the Trump campaign and Russian operatives.

A spokesperson for the data analytics firm’s former business development director, Brittany Kaiser, said she was subpoenaed by Mueller, according to a report in the Guardian, and was also assisting in ongoing Congressional investigations.

“This is the first evidence that a significant player in theLeave.EU campaign is of interested to the global Mueller inquiry,” the report cited Labour Party Deputy Leader Tom Watson as saying. Kaiser told parliament last spring that Cambridge Analytica had done significant work forLeave.EU.