The UK’s Serious Fraud Office has abandoned a criminal investigation into the Kazakh mining group ENRC, ending a decade-long corruption inquiry mired in controversy. The SFO updated its website on Thursday with a notice that it had closed the case after concluding there was “insufficient admissible evidence” to prosecute the company. In a series of updates released on the same day, the agency said it had dropped three other investigations, including an inquiry opened in 2017 into suspected corruption involving the Anglo-Australian mining company Rio Tinto. The decision to end multiple high-profile investigations comes as the SFO’s director, Lisa Osofsky, prepares to step down from the embattled agency in September and hand the reins to a former Metropolitan police chief. Closure of the case against ENRC concludes a complex investigation that has hung over the agency and led to a bitter legal battle over its handling of the inquiry. Launched in April 2013, the SFO’s investigation focused on allegations of bribery and fraud relating to ENRC’s acquisition of mining contracts in Africa. In 2021, the company – which was co-founded by three Kazakh oligarchs – brought a £70m lawsuit against the SFO at the high court, alleging the agency had mishandled the investigation and committed misfeasance in public office. Although the agency was largely cleared of wrongdoing in the case last year, other aspects of its conduct were criticised by the judge and it faces civil proceedings relating to ENRC’s claim. The anti-graft group Spotlight on Corruption raised concerns that ENRC’s civil litigation may have contributed to the SFO’s decision to drop its case. Helen Taylor, a senior legal researcher at the group, said: “The SFO should clarify whether the multiple legal actions the agency and its staff have faced from ENRC played a role in this decision. “Concerns have been raised that the litigation around this investigation has had a chilling effect on public scrutiny of the company’s conduct and closed down the opportunity for those affected by alleged corruption to have their voices heard in court.” An SFO source said the litigation had not influenced its decision. In the update to the case profile on the SFO’s website, the agency explained the investigation into ENRC had been dropped due to a lack of evidence that could be admitted into court. “As a responsible prosecutor, we must ensure all our cases meet the stringent evidence and public interest tests set by the code for crown prosecutors,” it stated. “Following our latest review of the investigation, we concluded that we have insufficient admissible evidence to prosecute, and closed the case.” A spokesperson for the mining group said: “ENRC is pleased that the SFO has finally closed its investigation and that the SFO is taking no further action in respect of this matter.”