In California you can record without consent if you have reasons to suspect a crime is going to be committed. It's not the most straightforward thing to get away with and you should work with a lawyer before you do it to be sure it will be accepted as evidence, but you can totally do it.
Laws that make something legal or not conditional on a hypothetical that hasn't happened yet are kind of lowsy. It's like the stand your ground one's where you can just say you believed your life was in danger.
I'm not implying anything, just criticizing laws where guilt or innocence rests on claim of a hypothetical situation. Shooting someone when you believe your life may be in danger. One party consent recording allowed when you believe a crime may happen.
There's always the risk of being caught while doing it, or to be exposed that you've done it before the time that you intend to "reveal" it.
So it's better to talk with a laywer and get informed of your options and the risks, and how to go about it, before you do it, not merely before you reveal you did it.
