By the time Dror Moreh had finished filming more than 70 hours of interviews with six former chiefs of Israel's shadowy Shin Bet secret service agency, the director knew he had "dynamite in my hands".
The result, The Gatekeepers, a 97-minute documentary which has just opened in the UK, is indeed explosive. The Oscar-nominated film has played to packed audiences in Israel, many of whom emerged stunned at what they had seen and heard.
"I thought if I could manage to get all [six] to speak openly about their experience in the Israeli-Palestinian conflict, it will create a shockwave," Moreh told the Observer. "I was right – it created a huge storm."
The recollections and reflections of the former chiefs weave a riveting narrative of Shin Bet's activities throughout Israel's 46-year occupation of the West Bank, Gaza and East Jerusalem. But the punch comes from their conclusions. "We are making lives unbearable," says Carmi Gillon; "We have become cruel," says Avraham Shalom; "You can't make peace using military means," says Avi Dichter; "We win every battle, but we lose the war," says Ami Ayalon.
"I was surprised at the extent to which they think in this way," said Moreh. "They are all saying: enough of occupation. They are not saying it's easy to reach a solution, but they all say it's in the best interests of Israel to pursue that."
It is the first time the six men, who ran Israel's intelligence operations in the Palestinian territories for almost 30 years, have given in-depth interviews. Much of the film's potency comes from their cumulative testimonies; "the power of six is more than the power of one," as Moreh put it.
The film opens with footage, presumably filmed from an Israeli military aircraft or unmanned drone, of a targeted assassination. A Palestinian vehicle is tracked before being destroyed in a blast. The urgent question, says Yuval Diskin, is to "do it or not do it. 'Don't do it' seems easier, but it's often harder."
Later the movie dissects the killing of Yahya Ayyash, the Hamas bomb-maker known as the Engineer, who was behind numerous suicide attacks in the early 1990s, by remotely detonated explosives concealed in a mobile phone as the militant spoke to his elderly father. The security chiefs also discuss dilemmas over approving operations that may result in the deaths of innocent family members or passersby.
Sometimes, says Diskin, "it's a super-clean operation. No one was hurt except the terrorists. Even then, later, life stops – at night, in the day, when you're shaving, we all have our moments, on vacation. You say: 'OK, I made a decision, and X number of people were killed. They were definitely about to launch a big attack, no one near them was hurt, it was as sterile as possible.' Yet you still say: 'There's something unnatural about it.' What's unnatural is the power you have … to take their lives in an instant."
Over original footage and computer-generated sequences, the former spy chiefs describe methods of controlling the Palestinian population, intelligence-gathering, interrogation techniques and Jewish extremism. The assassination of Israeli prime minister Yitzhak Rabin by a Jewish gunman opposed to the peace process is recalled as a major crisis for the Shin Bet. Gillon, the head of the security service at the time, describes coming to terms with the agency's failure to protect the country's political leader. He offered his resignation after consulting his wife. She, he says, just "tries to keep me alive".
Another crisis, the hijacking of "Bus 300" in 1984, ended with two Palestinian militants being beaten to death in the custody of the Shin Bet. Shalom, who was in charge at the time, is initially reluctant to discuss it, saying he does not remember the details of the episode which eventually forced his resignation.
Then, chillingly, he says: "They were almost dead. So I said: 'Hit them again and finish it.' I think he took a rock and smashed their heads in." It was, he admits, "a lynching", but adds: "In the war against terror, forget about morality."
Asked how he persuaded the six men to participate in the film, Moreh said he did not tell them in advance what the message would be "because I didn't know what the message would be. I just said I wanted to tell the Israeli-Palestinian conflict from the point of view of the people who have experience of the decision-making. No one could say they do not understand what they are speaking about. And I think they understood why their position, as heads of Shin Bet, will matter."
There is no narration in the film, just the voices of the six men with occasional questioning from Moreh. "I came to hear them, I was very interested in what they had to tell me. It was very important for me to listen, and just to navigate these long conversations."
There were many interviews, lasting four to five hours and mostly conducted in their homes – "in their environment, in the places where they feel most secure, to make them feel comfortable and allow them to open". They were not ingenues, says Moreh. "They understand the power of the tongue, the power of language, because they used that all their lives."
After the film opened in Israel, Moreh was accused of selectively editing his material. Moshe Ya'alon, now Israel's defence minister, told Army Radio: "What was presented there was presented in a really one-sided manner, and therefore the film is slanted. [Moreh] took parts of long interviews and presented the clips that served his narrative."
Moreh, who described his personal political viewpoint as centre-left "but more centre than left", rejected the allegation. "One of the most important things was not to take their words out of context, not to distort what they had to say on such delicate matters. And since the first screening of the movie, not one of the six has said it twisted what he had to say. For some, it was very tough. But all six stand firmly behind the message of the movie."
But should they have raised their voices earlier, when still in a position to influence policy? "They are professionals, they have a duty to protect Israel. They are not elected politicians, but appointed officials. As such they cannot criticise political [decisions] in a democratic society. Those who are public servants, if they don't feel they should do something, they should resign. This is what they answered when I asked them why didn't you say then what you are saying now."
Since retiring from their posts, three of the six have entered politics as members of the Israeli parliament. Ami Ayalon represented the Labour party from 2006 until 2009, Avi Dichter the centre-right Kadima party from 2006 until 2012. Yaakov Peri was elected in January's election to represent the centrist Yesh Atid party and is the current science and technology minister.
Towards the end of The Gatekeepers, Peri speaks over footage of a Shin Bet raid on a Palestinian home. He describes operations in which suspected militants are dragged from their terrified and sobbing families in the dead of night. Even when you know the details of what people have done, you have some doubts, he suggests. And then, "when you leave the service", he adds haltingly, "you become a bit of a leftist".
To Diskin, the most recent incumbent of the post, Moreh quotes the words of the late Israeli intellectual Yeshayahu Leibowitz, written soon after the start of the occupation. Ruling over the Palestinians, said Leibowitz, would effectively turn Israel into a police state, "with all that this implies for education, freedom of speech and thought, and democracy".
"I agree with every word," says the former Shin Bet chief.