They have assassinated Palestinians, incarcerated thousands and disrupted the lives of many thousands more - but they have become the most persuasive advocates in Israel for peaceful relations with an independent Palestinian state.
In a remarkable documentary The Gatekeepers, short-listed for best foreign documentary at the upcoming Academy Awards, Israeli film-maker Dror Moreh interviews six former heads of the Israeli Shin Bet security service.
They are unapologetic for the harsh steps their job has called for in suppressing Palestinian uprisings and suicide bombings. But all condemn the political level for failing to take advantage of the periods of relative tranquillity, like the present one, to seriously pursue a political accommodation. Their ire appears to be directed particularly at Prime Minister Benjamin Netanyahu.
"We win every battle but we're losing the war," said Ami Ayalon, 67, a decorated war hero who headed the Shin Bet between 1995-2000. As a child, he was told by his parents that in Jerusalem there was a building with a long corridor on the second floor, which led to a door behind which sat a wise man thinking about what the people need.
"I reached that corridor [leading to the Cabinet room] but there was no door and no wise man."
Avraham Shalom, 85, said that after the Six Day War he and others favoured the creation of a Palestinian state. "But then the terror started and we were so busy fighting it we forgot about the Palestinian state."
It was incumbent on Israel to try to talk to its enemies, even Hamas and Islamic Jihad. "And if they answer rudely to try again. It's too great a luxury not to speak to our enemies."
Avi Dichter (2000-05) said that peace was not built by military means. "There doesn't have to be a problem creating genuine relations of trust with them."
Carmi Gillon, whose tenure was cut short by the assassination of Prime Minister Yitzhak Rabin in 1995, spoke of the suffering caused by the Israeli occupation. "We are making the lives of millions insufferable."
Yaacov Peri (1988-94) spoke of night-time raids on the homes of Palestinian families. "Those memories make you a bit of a leftist."
Yuval Diskin (2005-2011), quoted from a text written in 1968 by philosopher Yeshayaha Leibowitz of Hebrew University in Jerusalem. "A country that controls a hostile population will necessarily become a Shin Bet state, with implications regarding freedom of speech and thought and democratic governance. The corruption characterising every colonial regime will also infect the State of Israel. The Administration will have to suppress Arab rebel movements and cultivate Arab traitors."
To which Diskin said "I agree with every word."