LONDON — A British codebreaker had complained of friction at the country’s overseas spy agency before his naked and decomposing body was found inside a padlocked sports bag, his family told an inquest Monday.

Gareth Williams worked for Britain’s secret eavesdropping service GCHQ and was attached to the country’s MI6 overseas spy agency when he was found in the bathtub of his central London home in August 2010. While detectives have suggested Williams, 31, may have died in a sex game gone wrong, his family has suggested that British spy agencies were involved in the death.

Williams’ sister Ceri Subbe told an inquest into his death that her brother was unhappy with the “rat race” in London and had requested to be sent back to GCHQ’s headquarters in Gloucestershire, western England

“The job was not quite what he expected,” Subbe said. “He encountered more red tape than he was comfortable with.”

The inquest’s central focus will investigate whether Williams could possibly have climbed inside the sports bag and locked it from the inside.

There were no signs of struggle, and no drugs or poison in Williams’ body, the discovery of which launched a media frenzy and flurry of conspiracy theories.

Experts consulted by police said Williams could not have locked himself inside the bag.

Police have made no arrests in the case and are still not certain exactly how Williams died. But Scotland Yard raised the possibility that criminal charges could still arise, telling the inquest Monday that it objected to the release of some material to the media because that could prejudice future criminal proceedings.

Subbe told the inquest Monday that she did not believe her brother would let a potential killer in his flat, saying he was extremely conscientious.

Her testimony came after the coroner leading the inquest agreed to allow four intelligence agents to give evidence anonymously.

Coroner Fiona Wilcox acknowledged “there will be a real risk of harm” to national security and international relations if the identities of some of those giving evidence at the inquest are exposed.

In Britain, inquests must be held when someone dies unexpectedly, violently or from unknown causes. However, the coroner’s task is to determine the cause of death, rather than to identify any suspect.