Page told a closed-door joint session of the House Judiciary and Oversight committees in mid-July that investigators could not make the charge, according to a transcript of her deposition reviewed by Fox News.
'I think this represents that even as far as May 2017, we still couldn't answer the question,' Page said.
In May 2017, Mueller was appointed by Deputy Attorney General Rod Rosenstein as special counsel overseeing an ongoing investigation into Russian interference in the 2016 election.
Trump and his Republican allies are likely to use this revelation to boost their argument the president is a victim of a witch hunt and the investigation has been tainted by politics.
But her testimony refers to a point in the investigation from over a year ago and it's unclear where the probe stands now.
Mueller has been tight-fisted with his look into Russia election tampering and has given no interviews.
But, since his appointment, his team has secured cooperation and plea deals from Trump players former National Security adviser Michael Flynn, former campaign chairman Paul Manafort, Manafort deputy Richard Gates and former campaign adviser George Papadopoulos.