Jerusalem - Fadi al-Qatshan is one of the latest casualties of a war taking place in Gaza's shadows, as Israel seeks ever more desperate ways to recruit collaborators while Hamas, the Islamic movement ruling Gaza, enforces tough counter-measures.

The 26-year-old graduate died in November. He was killed not by a bullet or in a missile strike, but when a simple piece of medical hardware - an implant in his heart - failed. His repeated requests to the Israeli authorities over more than a year to be allowed out of Gaza for medical treatment had gone unheeded.

According to his family, Israeli security services knew his life was in danger but denied him a permit to attend a medical appointment at a hospital in East Jerusalem. Gaza's own hospitals, in crisis after years of Israel's blockade, warned him they could no longer help.

Following a request for a travel permit, his family says al-Qatshan received a call from someone identifying himself as from the Shin Bet, Israel's intelligence service. Speaking in Arabic, the man said he knew the device in his heart "might explode any minute". He was urged to "cooperate" in return for a permit.

Al-Qatshan was told he could call the mobile phone number on his screen and arrange an appointment at Erez, the Israeli-controlled crossing that is the only way for ordinary Palestinians to exit Gaza. The agent reportedly rang off with the words, "See you in Tel Aviv", Israel's large coastal city. Al-Qatshan sealed his fate by deleting the number.

'Terrible choices'

Issam Yunis, director of Al-Mezan human rights organisation in Gaza City, says his group regularly records cases of Palestinians in desperate need of medical treatment being approached to collaborate. "The choice for these patients is really a terrible one. It is to cooperate with Israel or die in Gaza."

Although Israel is suspected of recruiting tens of thousands of Palestinians as collaborators since its creation in 1948, the practice has rarely attracted more than superficial attention. Palestinians are ashamed that cooperation with the Israeli security services is widespread, while Israel is loath to draw attention to the systematic violations of international law at the root of its system of rule in the occupied territories.

The choice for these patients is really a terrible one. It is to cooperate with Israel or die in Gaza. - Issam Yunis, director of Al-Mezan human rights organisation

But the issue of collaboration is finally emerging from the shadows, assisted in recent months by a spate of films addressing the subject.

In the running for an Oscar at the Academy Awards ceremony next month is Omar, a Palestinian film that places the awful dilemmas faced by collaborators at the heart of its love story.

Omar nudged out of the competition Israel's own entry, Bethlehem, which features a similar story about the fraught relationship between a Shin Bet agent and a young Palestinian informant.

And last month the audience award at the Sundance Festival went to the Green Prince, an Israeli documentary based on the memoirs of Mosab Hassan Yousef, son of a Hamas leader in Gaza who channeled information to the Shin Bet for 10 years before fleeing to the United States. His father, Sheikh Hassan Yousef, was recently released from an Israeli prison.

With Palestinian collaborators a hot topic in Hollywood, they are also in the spotlight in the occupied territories.

A missile strike that killed Hamas military leader Ahmed Jabari in November 2012 - the opening salvo in Israel's eight-day attack on Gaza known as Operation Pillar of Defence - has been widely ascribed to intelligence provided by a collaborator.

In response, Hamas carried out public executions of several suspected informants in the streets of Gaza City, including dragging the body of one behind a motorbike.

'Tightly classified'

According to Hillel Cohen, who has researched Israel's recruitment of collaborators since the state's earliest years, the extent of the problem is difficult to assess. Israel keeps most of the archives on its intelligence operations in the occupied territories "tightly classified".

The use of collaborators, he says, was probably most extensive in the 1970s and '80s, before Israel handed over areas of the occupied territories to the Palestinian Authority under the Oslo Accords and before the advent of today's more sophisticated surveillance technology.

Nonetheless, the practice has far from ended.

"Israel still needs people on the ground," says Cohen. "If they want to place a bomb in a car or supply a phone with a hidden tracking device, someone has to do it. The technology can only help so much."

According to Saleh Abdel Jawwad, a politics professor at Bir Zeit University in the West Bank, there are many different types of collaborators.

In East Jerusalem, for example, where Israel hopes to prevent any future Palestinian control of the city, a feature of life are the "land dealers", Palestinians who buy land in strategic areas, secretly on behalf of settler organisations.

Israel also uses economic collaborators, who, for example, act as contractors for Israel in selling its products in the occupied territories. Israel has also tried to recruit political collaborators, in an effort to place them in charge of Palestinian communities or weaken candidates Israel opposed.

But Israel prizes most highly the recruitment of active members of Palestinian national organisations, who can provide reliable information on resistance operations or the movements of Palestinian leaders.

Typically, these collaborators are "turned" after their arrest. They may agree to cooperate under torture or as a way to receive a reduced prison sentence, said Morad Jadalah, a researcher with Addameer, a prisoners' rights organisation in the West Bank city of Ramallah.

Children recruited

But the most common type of collaborator is the informant, who provides general information about the activities of political groups or the movement of individual activists, as well as the names of those taking part in demonstrations.

Jadalah says when Palestinians are arrested, as they try to cross a checkpoint or during a raid on their village, the weakest and most vulnerable - often children - are targeted during interrogation with a mix of threats, violence and inducements.

Long jail terms and the use of administrative detention - imprisonment on secret charges - are the most obvious threats, but there are other ways to pressure Palestinians in detention, says Jadalah.

"The interrogators may beat them, or threaten to beat or rape their mother or sister, or arrest a close relative. They usually already know something about the family, so they can threaten, for example, to revoke the father's work permit. They may even threaten to spread rumours that the family are already acting as informants."

In other cases, the Israeli security services may offer inducements. "Israel controls most people's lives, including their ability to work and move around. Between 30 and 40 per cent of adults are unemployed. That gives Israel the leverage it needs to recruit collaborators."

According to Jadalah, the Israeli security services usually want general information about the neighbourhood where the collaborator lives, or details about a specific person.

Reports suggest in recent years the Shin Bet has been using arrested children to gain information about the leaders of non-violent resistance movements in the West Bank. They have shown special interest in villages such as Bilin, Nabi Saleh and Budrus where well-publicised protests are trying to stop Israel's efforts to build the separation barrier on Palestinian land.

Cohen says the benefit to Israel of controlling an extensive network of collaborators is not limited to the information they pass on.

"It encourages the atomisation of Palestinian society. It fosters mistrust within the society and between members of the political movements. When everyone becomes a potential suspect, political passivity is encouraged. That is, in fact, the main goal."

'Infiltrated society'

Yunis, of Al-Mezan, agrees: "We are an infiltrated society. When there is so much suspicion, organised and effective resistance to the occupation becomes extremely hard."

In addition, Jadalah blames the Palestinian Authority for setting a bad example. "When it is clear that our leaders are working with Israel on 'security cooperation' and that they look to Israel for protection, a very powerful message is sent to Palestinian society that only Israel can offer such guarantees."

Hamas, apparently fearful of its inability to organise in the face of extensive collaboration, has officially waged war on Gaza's informants.

Early last year it offered a brief amnesty to existing collaborators, many of them recruited before Israel's 2005 disengagement, allowing them to turn themselves in in return for lenient sentences and financial help for their families. However, it has vowed a policy of zero tolerance since.

Faced with a shrinking pool of collaborators in Gaza, says Yunis, Israel has increased its use of electronic surveillance, especially drones. But it has sought new ways to recruit collaborators too.

That includes exploiting increased opportunities to reach Palestinians in Gaza indirectly, through social media. In particular, youngsters, often those without jobs or whose families are in dire need, are approached via Facebook or receive a call to their mobile phone.

"The caller might introduce himself as a businessman and says he can help them to get a permit out of Gaza. Once they attend the meeting, they are ensnared," says Yunis.

Fishermen are also reported to have been targeted since Israel tightly limited the extent of the waters they are allowed to fish. When they cross out of that zone, they can be picked up by a naval patrol and taken for interrogation in Israel. There they can be pressured to turn informant.

'Desperate' situation

But the most wrenching cases, says Hamdi Shaqura, director of the Palestinian Centre for Human Rights in Gaza, occur with patients such as al-Qatshan who need urgent medical treatment.

Because they are among the few cases that Israel still treats as humanitarian, they and the relative that accompanies them present the Shin Bet with a rare opportunity to try to recruit a collaborator directly.

"These permits from Israel become a tool for blackmail. It is a serious violation of international law. Because Israel still occupies Gaza, the welfare of these patients is fully its responsibility. Israel is obligated to facilitate their movement and access to proper healthcare."

According to the World Health Organisation, about 150 patients from Gaza were called for a security interrogation by the Shin Bet last year, including a 16-year-old girl in November. In most cases they were denied a permit afterwards.

"When things are so desperate, it is easier to persuade the family, including the children, to continue working for the intelligence services." - Yadin Elam, Israeli human rights lawyer

Israel also arrested five patients at Erez and six of their companions over the course of last year. They included Mohammed Saber Abu-Amsha, a 33-year-old patient with damage to his eyes, who has been held in prison in Israel since his arrest on December 4.

Amal Ziada, a researcher for Physicians for Human Rights in Israel, said her organisation was hoping to launch a new campaign to raise awareness among the Israeli public of the pressures being used against medical patients.

That included lobbying members of the Israeli parliament and taking high-profile cases to the Israeli supreme court.

"What these patients go through is a kind of torture," she said. "The danger is that some of them avoid seeking medical treatment because they are afraid. They are worried about being arrested, or the suspicion among other Palestinians that they may have collaborated if they receive a permit."

Guy Inbar, spokesman for COGAT, the Israeli military unit that coordinates civilian matters in the occupied territories, said he awarded permits to Palestinians for medical treatment based only on medical need and the applicant's security record.

A senior Israeli security official said the accusation that Israel used the permit system to recruit collaborators was "baseless". "There have been many recent instances where terror organisations have manipulated people needing humanitarian help so that they assist in carrying out terror operations."

According to an Israeli human rights lawyer, Yadin Elam, most of the collaborators whose cover is blown and manage to flee the occupied territories do not receive the warm welcome in Israel they may have expected.

Israeli authorities divide collaborators into two groups, he says. Important collaborators, categorised as sayanim, or helpers, fall under the responsibility of the defence ministry and receive a salary and status inside Israel.

But most collaborators who reach Israel - numbering a few hundred, according to Elam - are classified simply as "threatened people", referring to the fact that they might be killed if they return to Palestinian areas.

Elam says Palestinians in this latter category are usually left in a desperate situation, sometimes given a temporary permit to stay for a few months, but denied permits for their immediate family or the right to work. Typically they live underground in Israel with their families and drift into crime.

Elam says these collaborators' insecurity, and their frequent arrests, provide an ideal opportunity for Israel to keep up the pressure.

"When things are so desperate, it is easier to persuade the family, including the children, to continue working for the intelligence services."