A second 'Prisoner X' was being held in top-secret conditions in the same jail where an Israeli-Australian spy took his his own life in 2010, a newspaper reported on Tuesday.
Court documents cited by Haaretz newspaper said the prisoner was being held in another wing of Ayalon prison at the same time as Ben Zygier, an alleged Mossad spy whose mysterious arrest and subsequent suicide shocked Israel and Australia when it hit the headlines in February.
The documents show the second prisoner had already been convicted without saying what his crime was.
The prisoner, who was being held under similar conditions to Zygier, was not named and it was not clear from the papers whether he was still incarcerated, Haaretz said.
Zygier, who was initially referred to as "Prisoner X" before the Australian press identified him as an agent for Israel's shadowy Mossad spy service, was found hanged in a supposedly suicide-proof cell in Block 15 of Ayalon prison in December 2010 with Israel going to extreme lengths to cover up his existence and the reason for his imprisonment.
Haaretz said the second prisoner was being held in Block 13 and that like Zygier, his case was being handled by the Shin Bet internal security service and the prison's intelligence officers.
The paper said the information was included in an appendix to a transcript of hearings and decisions on the Zygier case, which was released by the Central District Magistrates Court following a Haaretz request.
Avigdor Feldman, a lawyer who visited Zygier just days before his death and who specialises in security cases, told army radio that certain assumptions could be drawn from a detainee being classified as 'prisoner X.'
"They are Israeli, they work in institutions linked to security whose activities are shrouded in secrecy," he said.
"And their detention demonstrates the failure of these organisations which are not capable of preventing offences such as those for which these agents have been arrested," he said.
Two months ago, the Australian Broadcasting Corporation, which broke the original story about 'Prisoner X' in February, said that Zygier had been arrested after unwittingly sabotaging a top-secret spy operation to bring home the bodies of Israeli soldiers missing in Lebanon.