By applying pressure to law enforcement. Maybe by working hard to empanel a grand jury (though I have no idea how that works, and from what I’ve been told it goes through politicians so it’s nearly hopeless unless you can apply so much pressure that even a politician would respond).
The only other legal option for us in this regard is passing laws that enable grand juries or prosecutions without politicians as gate-keepers - which is what I thought. I don’t know anything more about how that would work.
If a person caught him in the act they could make a citizen’s arrest, if I understand correctly. But that doesn’t work on crimes already committed.
“by working hard to empanel a grand jury...(...from what I’ve been told it goes through politicians so it’s nearly hopeless unless you can apply so much pressure that even a politician would respond).”
Perhaps a Five Million Citizen March would be enough to get their attention.