Google said in a statement Mitchell violated the company’s code of conduct and security policies by moving electronic files outside the company. Mitchell, who announced her firing on Twitter, did not respond to a request for comment.

Google’s ethics in artificial intelligence work has been under scrutiny since the firing of Gebru, a scientist who gained prominence for exposing bias in facial analysis systems. The dismissal prompted thousands of Google workers to protest. She and Mitchell had called for greater diversity and inclusion among Google’s research staff and expressed concern that the company was starting to censor papers critical of its products.

Gebru said Google fired her after she questioned an order not to publish a study saying AI that mimics language could hurt marginalized populations. Mitchell, a co-author of the paper, publicly criticized the company for firing Gebru and undermining the credibility of her work.

The pair for about two years had co-led the ethical AI team, started by Mitchell.

Google AI research director Zoubin Ghahramani and a company lawyer informed Mitchell’s team of her firing on Friday in a meeting called at short notice, according to a person familiar with the matter. The person said little explanation was given for the dismissal. Google declined to comment.

The company said Mitchell’s firing followed disciplinary recommendations by investigators and a review committee. It said her violations “included the exfiltration of confidential business-sensitive documents and private data of other employees”. The investigation began Jan. 19.

Google employee Alex Hanna said on Twitter the company was running a “smear campaign” against Mitchell and Gebru, with whom she worked closely. Google declined to comment on Hanna’s remarks.

Google has recruited top scientists with promises of research freedom, but the limits are tested as researchers increasingly write about the negative effects of technology and offer unflattering perspectives on their employer’s products.

Reuters reported exclusively in December that Google introduced a new “sensitive topics” review last year to ensure that papers on topics such as the oil industry and content recommendation systems would not get the company into legal or regulatory trouble. Mitchell publicly expressed concern that the policy could lead to censorship.

Google reiterated to researchers in a memo and meeting on Friday that it was working to improve pre-publication review of papers. It also announced new policies on Friday to handle sensitive departures and evaluate executives based on team diversity and inclusion.