The most expansive of the many provocative assertions in The Gatekeepers, Dror Moreh's Oscar-nominated interrogation of six former heads of Shin Bet, Israel's renowned intelligence agency, is that Shin Bet men age to the left — and become more critical of Israel. Why this might be so is the larger subject of Moreh's searching, engrossing, and stylish inquiry, another contribution to the informal truth and reconciliation campaign being waged by a growing number of Israeli filmmakers. Politicians, says Yuval Diskin, Shin Bet's leader from 2005 to 2011, prefer their problems distilled into binaries so that binary solutions might follow. But the Israeli occupation of Gaza and the West Bank, which began in the wake of 1967's Six-Day War, has produced endless problems in infinite shades of gray. Diskin, just a boy when that war took place, joined Shin Bet as a proud young man, wanting to be part of the solution. What he and the others here describe is their moral and political evolution as occupiers and the devolution they believe is threatening Israel from within. It makes for compelling viewing, but the enigmatic cross-hatching of insights that emerges from those big interviews makes The Gatekeepers something more essential. You don't get the sense that it's any easier for these men to question Israel's leadership, or lack of leadership, from the safety of retirement. All of them insist that continuing to talk to Palestine is the only option; only Avraham Shalom, the eldest, goes further. "We have become cruel to ourselves but mainly to the occupation," he says.