In 2015 Emmerson represented Marina Litvinenko, wife of Russian ex-KGB agent Alexander Litvinenko, at the public inquiry into his murder in London in 2006, using a radioactive isotope, (Polonium 210). Emmerson argued a successful judicial review challenge to the British Government's refusal to hold a public inquiry to examine the responsibility of the Russian State for Litvinenko's murder. According to Chambers UK, "forcing a public inquiry [was] down to the sheer force of his personality". At the completion of the public inquiry, the judge, Sir Robert Owen, found that the Russian State was responsible for ordering the murder, and that Russian President Vladimir Putin had "probably" given his personal approval to the killing. Following the publication of the Inquiry report, Emmerson described the murder as an act of "nuclear terrorism" and called on Prime Minister David Cameron to take effective action, saying that a failure to respond would be a "craven" abdication of his responsibilities. An official spokesperson for the Prime Minister commented: "The conclusion that the murder was authorised at the highest levels of the Russian State is extremely disturbing" and promised to take effective action in response.