Special counsel Robert Mueller is seeking answers from a second former employee of data firm Cambridge Analytica as his team investigates allegations of collusion between the Trump campaign and Russia.

According to The Guardian, Brittany Kaiser — who was a business development director for the analytics firm before it closed in May 2018 — received a subpoena from Mueller's team. She is reportedly cooperating with the probe.

Kaiser's spokesman confirmed to the news outlet that she is also working with other U.S. investigations, including those in Congress, into the 2016 election collusion claims.

Cambridge Analytica worked on more than 200 elections across the world between 2013 and 2018. It's work during the 2016 U.S. presidential campaign has come under intense scrutiny.

It was reported last year that the firm mishandled data belonging to more than 50 million Facebook users as President Donald Trump was campaigning for office.

The firm has also been accused of trying to partner with WikiLeaks to hunt for Democrat Hillary Clinton's 33,000 emails that were deleted after she served as secretary of state. The Trump campaign contracted with the company to obtain digital data.