The tidbits released by the police and the Shin Bet read like something from a classic spy novel. In 2012, they said, contact had been made between Mr. Segev and people from Iran’s embassy in Nigeria. The first contact was with Iran’s agricultural attaché in Nigeria. Mr. Segev’s biography on the website of the Israeli Parliament lists his profession as “agriculturalist.”

Image Gonen Segev Credit... Israeli Government Press Office, via Reuters

According to the Shin Bet, he was recruited to work as an agent for Iranian intelligence.

Mr. Segev is said to have traveled to Iran twice to see his handlers and met them in hotels and apartments around the world. He received secret communications equipment for encoding messages between him and his handlers, according to the statement by the Israeli authorities.

“Segev transferred to his handlers information on — inter alia — the energy economy, security sites in Israel, and diplomatic and security personnel and buildings,” the statement said. Explaining how Mr. Segev may have gained access to up-to-date information, despite his criminal record and sojourn in Africa, the Israeli authorities said he had maintained contacts with Israeli citizens in the foreign affairs and security fields and worked to put some of them in contact with Iranian intelligence agents by “misleading the former and presenting the latter as innocent Iranian businessmen.”

Mr. Segev may be the most prominent Israeli to date to be publicly suspected of espionage for the Iranians. But it is not clear that Mr. Segev had much to offer.

“The truth is that he was uninformed about anything and he was in touch with only a handful of people because people know who he is and didn’t cooperate with him,” wrote Nir Dvori, the military affairs correspondent for Hahadashot television news, on the station’s website. Mr. Dvori said Mr. Segev had acted out of financial distress.

Eli Zohar and Moshe Mazor, lawyers who are representing Mr. Segev, said in an emailed statement: “We have been accompanying Mr. Segev since the date of his arrival in Israel about a month ago. An indictment was recently submitted, the details of which are overwhelmingly classified at the state’s request. At this preliminary stage one can already say that the publication that was approved lends a very severe semblance to the affair, even though the indictment, the full details of which are classified, as noted, paints a different picture.”

Mr. Segev, a medical doctor, had made a career for himself in the top rungs of Israeli public life. He was elected to Parliament in 1992 as a member of Tzomet, a right-wing party led by Rafael Eitan, a former chief of staff of the Israeli military. Breaking away with a few other legislators to form a new party, Yiud, he joined Yitzhak Rabin’s Labor-led government and served as minister of energy and infrastructure. He remained in the post for months after Mr. Rabin’s assassination, in the government led by Shimon Peres, until the 1996 election that first brought Benjamin Netanyahu to power.