The relatives of former KGB officer Alexander Litvinenko, who was poisoned in 2006 in London, have called for a substantial probe into his death, BBC reported on Thursday.
Marina Litvinenko, the widow of the late officer, urged a senior High Court judge to conduct the probe, BBC reported.
St. Pancras Coroner's Court in London on Thursday began hearings to establish Litvinenko's cause of death.
Earlier British authorities said that the hearings would be carried out behind the closed doors. The Russian Embassy in London however has insisted on an open trial.
BBC said that journalists were eventually allowed to enter the courtroom, but were prohibited from recording the trial.
Ben Emmerson, who represents Litvinenko's family, said that the case boosted "grave suspicion" that Litvinenko's death was the result of state-directed execution by Russia.
Litvinenko, an outspoken critic of then-president Vladimir Putin, died in November 2006 in a London hospital presumably after being poisoned with the radioactive substance polonium-210.