While it is tasked with hearing all the evidence to establish the truth of what happened to Ms Sturgess, the public inquiry cannot determine guilt or put anyone on trial.
Two Russian nationals, who arrived in the UK under the aliases Alexander Petrov and Ruslan Boshirov, were named by UK counter-terrorism police as suspects in September 2018. A third suspect, Sergey Fedotov, was named by police in February 2019.
All three men are thought to be members of the GRU, the Russian intelligence agency.
An international arrest warrant has been issued but unless they leave Russia it is unlikely they will ever stand trial – as the Russian constitution does not allow the extradition of its citizens.
The Russian government has always denied involvement in the incident. Its foreign ministry has described the inquiry as a “circus”.