The criminal trial of a prominent Russian physicist accused of state treason opened in St Petersburg on Thursday amid tight secrecy and concerns over the health of the elderly defendant.
Anatoly Maslov, 76, is one of three hypersonic missile scientists who worked at an institute in the Siberian city of Novosibirsk and who are now facing what the Kremlin has said are "very serious accusations".
The case, marked as "top secret", is closed to the media and public, the St Petersburg court has said
Maslov's lawyer could not be reached for comment on Thursday's hearing.
A source close to Maslov told Reuters the scientist had suffered two heart attacks and spent time in hospital since his arrest last June in Novosibirsk. Maslov was a professor and researcher at the Khristianovich Institute of Theoretical and Applied Mechanics, one of Russia's top scientific centres.
Soon afterwards, Maslov was sent to Lefortovo prison in Moscow, a former KGB interrogation site, before being transferred to St. Petersburg to stand trial.
Doctors in the pre-trial detention centre have not given Maslov access to all the medication prescribed by his normal physician, the source said, adding: "He's holding on, but of course, his condition isn't very good."
Reuters could not independently verify the accusation regarding the denial of medication.
All three defendants are specialists in hypersonics - a field of key importance to the development of Russia's next generation of missiles, capable of flying at 10 times the speed of sound.
Colleagues have said the prosecutions of the three men could damage Russian science.
Details of the accusations against them are classified, but the news portal of the science city where they are based said Maslov was suspected of handing secrets to China.
The source said Maslov maintains his innocence and "does not consider himself a traitor. He believes that he always did everything correctly."
Russia's parliament voted in April to increase the maximum penalty for treason to life imprisonment from 20 years.