JERUSALEM – An Israeli secret agent whose death in Israel's highest security prison was kept secret for nearly two years may have inadvertently revealed details of one of Israel's most important intelligence-gathering networks, according to new accounts of the case published Monday.

Why Mossad agent Ben Zygier, who was known until earlier this year only as Prisoner X, was jailed had been a lingering mystery. Zygier spent nearly a year in solitary confinement so rigid that not even his jailers knew his real name before he died, allegedly a suicide. Israeli officials added to the mystery by forbidding journalists from reporting on the case after Zygier was found dead in his cell in December 2010.

A wide variety of theories for his imprisonment had been floated, including that he'd sold intelligence to Iran, was preparing to publish a tell-all about the Mossad or had turned double agent for a government in the Persian Gulf.

But the new reports suggest that Australian-born Zygier was a desk-bound agent who botched a self-initiated effort to turn a Hezbollah operative into an Israeli agent, instead ending up revealing the identities of Israeli operatives in Lebanon.

According to Fairfax Media, Australia's largest newspaper publisher, and Germany's Der Spiegel magazine, which conducted a joint investigation into the case, Zygier unwittingly handed over Israeli intelligence files to a man he thought he was turning into a double agent for Israel.

Zygier, the news organizations claimed, thought that by turning the man into a double agent he'd win the approval of his bosses at the Mossad and be promoted within the spy agency. Instead, Zygier gave away information that included the identities of two of the Mossad's best informants in Lebanon.

Zygier, who grew up in Melbourne in a strongly Zionistic family, immigrated to Israel and was recruited to the Mossad in 2003. At first he worked in Europe, where he took an accounting job in a company with links to the Middle East. In 2007 he was ordered back to Tel Aviv and assigned to a desk job because his bosses were unhappy with his work, according to the Der Spiegel report, which was written by Israeli journalist Ronen Bergman.

Zygier used recently increased access to computer data, Bergman said, to try to recruit an Eastern European man known to be close to the Lebanese Shiite Muslim militant group Hezbollah.

In his attempt to recruit the man, Zygier revealed the names of Israel's top two Lebanese informants, Ziad al-Homsi and Mustafa Ali Awadeh. Soon afterward, the two men were arrested and sentenced to 15 years in prison.

Israeli officials have refused to comment on the details of the case, but it was revealed in a court file released earlier this year that Zygier had agreed to be held in jail under a pseudonym and that his lawyer was negotiating a possible deal that would include a 10-year jail term for his client. Zygier allegedly killed himself by constructing a noose in his shower in December 2010 just days after meeting with his lawyer to discuss the plea bargain.

While they couldn't confirm the Fairfax and Der Spiegel report, Israeli intelligence officers said that the story "rang true" and that it had long been rumored that a Mossad insider had bungled Israeli undercover operations in Lebanon.