it would be great if phones allowed you to store 2 different passwords. One to unlock the phone as normal, and the other would actually wipe the phone. Sure, officer, my password is "deleteitall"
What I want is a system that has two passwords that unlock two wholly separate partitions, one of which is anodyne and the other which is where I keep my private opinions about Big Brother.
Of course, astute investigators might wonder why the accessible partition only uses half the storage capacity of the device; you might wish to make your secret space very small and perhaps use some compression scheme as well. If you have a large amount of information that you wish to keep private, you're probably best storing it somewhere else entirely and only accessing it remotely.
Only if someone can prove the data was there in the first place.
If I put in my password and you get back a reset phone with no personal data whatever, then it's rather obvious that I've wiped it (eg my wallpaper picture has likely reset from my personal taste to the system default). So now you don't have the evidence to convict me of what you suspected me for, but you can bring another charge, and DoE charges will cause most people to assume that the original accusation/suspicion was well founded. If you are able to prove it by other means I'll get less sympathy from a jury and likely a much higher penalty.