ASHKELON, Israel — In the grainy security camera footage, Avera Mengistu walks along the beach on the Israeli side of the border, marked by a wall and netting. Then, suddenly, he appears on the other side, in Gaza.
“You don’t see how he got there,” said his mother, Agernsh, describing the video from the security services that she and other relatives saw, as tears rolled down her face. Filmed from a particular angle and possibly edited, the family said, the video left them with as many questions as answers.
Almost a year after the disappearance of Mr. Mengistu, a 29-year-old Israeli Jew of Ethiopian descent, his family remains mostly in the dark about his whereabouts or condition. The Israeli authorities say they believe he is alive and being held hostage by Hamas, the Islamic militant group that controls the Palestinian enclave.
Shifting gears, the family was planning its first public protest to be held Monday outside an Israeli prison where relatives of Palestinian prisoners were expected to visit. The demonstration would be one of a series of protest actions focusing on the humanitarian aspect of the case, according to representatives of the family.
Until now the family had called on the public to act with restraint and to give the Israeli authorities more time to work behind the scenes, fearing that a noisy public campaign may only raise the value of Mr. Mengistu in Hamas’s eyes, and increase the price for his return.
Israel said last month that Mr. Mengistu had crossed the border into Gaza independently, lifting an official gag order on the case and touching off a flurry of media attention.
But a haze of official secrecy continues to hover over the episode. The Mengistu family says it has received no new information on the case for the past month. Hamas has spread ambiguous hints and contradictory messages about Mr. Mengistu, demanding a price for any firm information and intentionally adding to the uncertainty.
The state’s handling of the case has also prompted accusations of racism in a country where the issue of Israelis in captivity is an emotional one, but where Ethiopian-Israelis have recently taken to the streets to protest against what they view as discrimination, police harassment and brutality. Some critics have argued that the case could not have been suppressed for so long had the missing person been from a stronger section of Israeli society.
Channel 10, a commercial television station, released a tape of the government’s coordinator for hostages and missing persons, Lior Lotan, berating the Mengistus for daring to ask Prime Minister Benjamin Netanyahu in a rare phone call why Mr. Netanyahu had not replied to their letters, and threatening them that blaming the government would only put off any possible release by a year. Mr. Lotan apologized.
But amid a storm of public criticism, Mr. Netanyahu rushed to visit the family on a Friday afternoon, shortly before the Sabbath, at their apartment in a rundown public housing project in this southern Israeli city about 10 miles up the coast from Gaza.
At the center of the case is a troubled man who was adrift long before he strode along the beach on Sept. 7, two weeks after a cease-fire took hold that ended 50 days of fighting between Israel and Hamas in Gaza.
Born in Ethiopia’s Gondar Province, Mr. Mengistu was airlifted to Israel with his family in 1991, at the age of 5.
The fourth of eight siblings, he went into first grade, proved “very clever,” said Yallo Mengistu, his oldest brother, and completed high school.
But Avera Mengistu, who has suffered from depression, was not drafted into the army at 18, like most Israeli Jews. He was given an exemption after a medical committee found him unfit to serve, according to documents provided by the family. His parents divorced and in 2011 another brother, Michael, who he admired and was close to, died of some form of anorexia.
After that, Mr. Mengistu’s depression worsened, according to his family. He lived with his mother and did odd jobs. He was hospitalized in psychiatric wards for a week or more twice in 2013, once voluntarily and once under an emergency commitment, according to Health Ministry records.
He had also gone missing for days at a time before he entered Gaza in September. Once, his family said, the police brought him home after he was found on a lonely shore by the Sea of Galilee in northern Israel.
On Sept. 7, at about noon, Mr. Mengistu arrived at the family apartment in an agitated state. “He was pacing and wrapped up in his own thoughts,” said Ilan, another brother. His mother went into the kitchen to cook, hoping he would calm down. Then she heard the front door slam. By nightfall, Mr. Mengistu had not returned.
The next day, Ilan Mengistu said, officers from the Shin Bet internal security agency called him, then came to him at work and told him that his brother had crossed the border into Gaza at around 5 p.m. the day before. He left behind a bag containing his identity card, a Hebrew Bible, a towel, slippers and a mathematics book, though his brothers said he was not known to be studying math.
Mr. Mengistu had never spoken much about Gaza, according to his relatives. During last summer’s war, militants fired thousands of rockets at Israel, more than 2,200 Palestinians were killed in Gaza and more than 70 were killed on the Israeli side, mostly soldiers. But Mr. Mengistu was “in his own world,” Ilan said, adding, “What was happening did not interest him.”
When Israel publicized Mr. Mengistu’s case, it said another Israeli citizen, a Bedouin Arab from the Negev desert who was not named, had also crossed into Gaza in recent months and was also believed to be in the hands of Hamas. Israel says Hamas is also holding the remains of two soldiers, Second Lt. Hadar Goldin and Staff Sgt. Oron Shaul, who were killed in action last summer.
The government has paid a high price in the past for the return of its citizens and soldiers, or their remains, in lopsided prisoner exchange deals. But the issue has become more politically charged since 2011 when Israel released more than 1,000 Palestinian prisoners, many of whom had been convicted of deadly attacks against Israelis, in exchange for Gilad Shalit, a soldier who was seized in a cross-border raid in 2006 and held captive by Hamas in Gaza for five years.
Gathered in Ilan’s small and simply furnished apartment for a recent interview, Mr. Mengistu’s family now seems torn between treading carefully with the Israeli authorities and not wanting to drive up Mr. Mengistu’s price, while appealing for mercy from Hamas and for international support.
In a rare public reference to Mr. Mengistu, a senior Hamas official, Moussa Abu Marzouq, denied Israel’s version of events, telling Al Jazeera’s website in a mid-July interview that Mr. Mengistu — who never served in the army — had been photographed in military uniform and suggesting that he was already in Gaza during the war last summer. He gave no hint of Mr. Mengistu’s whereabouts or condition, but he claimed that the Israelis were pretending that Mr. Mengistu was insane in an effort to lower his value.
“The story of my brother is a purely humanitarian one,” said Ilan Mengistu, noting that dozens of Palestinians who crossed illegally from Gaza into Israel have been sent back to their families. “There are many ways to solve conflicts,” he added, “but it is inconceivable that anyone with a drop of mercy in their heart would hold a man who is mentally ill.”
At the end of footage taken by the security camera, Yallo Mengistu said, two Palestinians can be seen in the sea and one on the beach on the Gaza side of the border.
“Avera speaks to the man on the beach for about 30 seconds,” he said. “Then he climbs up a hill and disappears.”