JERUSALEM — Prisoner X used at least four names: Ben Zygier, Ben Alon, Ben Allen and Benjamin Burrows. Raised in a prominent Jewish family in Melbourne, he immigrated to Israel as a young man and joined the Israeli Army, spending time on a kibbutz in the north.

And, according to an Australian news report, before his secret imprisonment and mysterious suicide in an Israeli maximum-security prison cell in 2010, he was one of several people being investigated by the Australian intelligence service, suspected of spying for Israel and using his passport for travel to Iran, Syria and Lebanon.

“You connect to people in different ways and I remember his blue eyes,” recalled Rivka Giland, the chairwoman of kibbutz Gazit, where Mr. Zygier was a frequent presence for a year or two about a decade before his death. “There was something in the way he looked — you know you see a young man sometimes in uniform and sometimes in civilian clothes — and he had smiling clear light eyes.

“Just like he arrived,” she added, “he then disappeared.”

One day after Mr. Zygier, a 34-year-old father of two, was identified by an Australian television report as Israel’s mysterious Prisoner X, Israel released its first official acknowledgment of the case, lifting a news media blackout of more than two years, and the Australian foreign minister ordered an investigation into his government’s handling of the detention and death.