That was my own interpretation... but admittedly maybe too strong of a statement. Maybe she would have be caught. That said, the psychological setup in those periodic interviews with a "maybe lie detecting machine" create opportunity to find real issues.

In terms of the details here, the leak wasn't to expose the crimes, it was to resist political pressure [my speculation anyways]. The crimes were being investigated anyways and the video was available internally fairly broadly (and I think maybe externally as well). There was a political storm as a result of the investigation and the arrests made. Apparently leaking the video is was not illegal (though that's subject to some interpretations) because the role of the chief prosecutor is independent but this became more complicated when it required lying to the supreme court to cover the leak.

But yeah, it's possible the Shin Bet already had an idea but just used the polygraph as an excuse/opportunity. While it's understandable in the political climate why the chief prosecutor would leak the video it's also unethical and poor judgement for someone in her role to do so, and then to cover it up. The role of the Shin Bet is to find people in sensitive roles who are secretly doing things they should not be doing (typically spies but more generally people betraying the trust put in them). For those not following, the plot got thicker because she proceeded to throw her iPhone in the Mediterranean and it was found by a swimmer some days later. She also tried to harm herself. It's pretty crazy stuff. Now there are arguments about who should oversee the investigation with the supreme court set to decide today. It's a pretty small/tight legal community and everyone knows everyone, especially at the top. The legal system has been in a battle with the government for some while with the justice minister refusing to accept the last appointment of the chief justice of the supreme court.

Anyways, the polygraph angle is interesting. That this machine survives as a practice in many places tells us something about its usefulness (or at least people's belief in its usefulness).

Maybe. The same can be said for placebo. But if it works - it works.

This is standard procedure for everyone in certain roles. Presumably for the same reasons the FBI does this.

Good carpenters can build stuff without nail guns, doesn’t mean it makes sense to use hammers.

No, because I would never talk to them.

Door locks are a deterrent that increase the difficulty and cost of a crime. If your neighbor's house is locked and yours isn't, then you're going to be more of a target. In that sense they do provide security, but of course any lock might still be defeated.

Similarly, I can see how structured psychological interrogation, assisted by a polygraph, is a useful deterrent. The presence of moles doesn't negate all of its value. Just like having your house broken into once doesn't mean you'll stop using door locks.