Digital Evidence Destruction

Doesn't this approach cast doubt on the legitimacy of any evidence obtained from the device?

Why isn't this considered destruction of evidence and thus a crime itself?

They don't need to know you have evidence. All they need to know is that you deliberately caused them to erase your device under the guise of unlocking it. Which means your device could have had evidence, and now you've made it impossible to prove that it didn't.

Not necessarily no evidence left behind, just no "smoking guns" that can be trivially discovered by private citizens without power of subpoena or warrant.

the state can't use the evidence against you in court, can it?

Forgive my query, but why is destroying evidence not seeing as admitting guilt?

If the victim has reason to belive their data would lead to a conviction the police wouldn't need to ask for it

I suspect we have different definitions of “legal system” in mind. You are correct that such things cannot be admitted as evidence into a court case, but law enforcement agencies still use the machines and do their best to lie to unknowing victims that it will be admitted to court.

You can claim that by having signal on your phone, it probably compromised the evidence gathering and you didn't know about it and you don't know how, so that evidence is not trustworthy. Kind of like police opening anti-tamper / anti-shoplifting seals which ruin the item they are trying to confiscate with a large amount of dye.

I guess the prospect of outside meddling will seem sufficiently unlikely that juries will not view it as much of a hindrance. After all, even with a chain of custody, there are innumerable opportunities for evidence to be planted. You just have to get one or two people who are willing to lie about things. In the US, the standard is "reasonable doubt," and the faint chance that evidence is tampered with during this unlock process will not likely trip the "reasonable" part of t