Information Haaretz has received in the past from Israel Prison Service officials sheds light on the conditions under which "Prisoner X number two" was held.

On Tuesday, the Rishon Letzion Magistrate’s Court heard testimony that another Israeli is being held in total solitary confinement in one of the most secure prisons in Israel - the same prison in which the Mossad agent Ben Zygier was held. According to the testimony, the cell is well guarded and without windows. The prisoner has no contact with other prisoners or with his guards, who know nothing of his identity or the details of the indictment against him.

According to prison service officials, except for brief walks in a secluded adjacent yard, the prisoner has not left his cell for a few years now. The yard is said to be surrounded by a high stone fence covered with heavy iron. Like the cell in which Zygier committed suicide, this prisoner’s cell is also monitored by cameras 24 hours a day.

Earlier on Wednesday, Knesset Foreign Affairs and Defense Committee Chairman Avigdor Lieberman called the case an "extremely severe incident" but maintained that Israel was acting within legal means.

During the committee's meeting, Lieberman criticized publication of the affair, but added that such arrests are being supervised: "Following all the talk about prisoners X, Y and Z, I want to emphasize that the State of Israel abides by the law and all these incidents are being closely supervised by the legal and parliamentary establishment through Foreign Affairs and Defense Subcommittee."

"Israel protects the rights of prisoners in accordance with the law. We handle the matter scrupulously, despite the severity of the case," Lieberman added.

News of an additional anonymous prisoner was discovered in one of the appendices to the transcription of the discussions and decisions made in the affair of Zygier the alleged Mossad agent whose incarceration and in-jail suicide was made public earlier this year.

President of the Central District Magistrate's Courts, Justice Dafna Baltman-Kardai, released the documents following an appeal by attorneys Tali Liblich and Yaron Shlomi.

Public Security Minister Yitzhak Aharonovitch also issued a statement on the case Wednesday, reiterating a statement he had made in February regarding Zygier: "There are no disappeared prisoners in Israel whose families don't know of their incarceration."

"The legal authorities do not handle their cases," he added. "Reports of each arrest are passed on to the relevant entities and are handled by the prosecution and courts, according to the law. Nonetheless, sometimes there are files whose existence cannot be released to the public, in order to present damage to state security. In these cases, a court gag order is imposed. There are also cases in which it is necessary to keep an inmate's name concealed to present damage to state security. Even in these cases, the prisoners' rights are meticulously protected, and these prisoners are certainly not 'hidden' from the courts."

On Tuesday, Attorney Avigdor Feldman, the last person to see Ben Zygier alive before he was found hanged in his cell in Ayalon Prison in 2010, said the offenses committed by this other inmate were far more severe.

According to Feldman, "this affair points to far more severe failures than the ones committed by the defense establishment in Zygier's case. Regarding Zygier's case, the authorities that recruited him didn't understand who they were dealing with and weren't aware of his conduct. Okay - that's a failure. Prisoner X number two is an entirely different story - a horrible security breach. When I heard the story, as an Israeli citizen I was shocked, and the subject was completely silenced by lawyers who enjoy close ties with the establishment. Whoever opens this affair will be doing the country a great service."