@Ancani obviously everyone here would want to see the letter, but that is only going to cause you more harm.
There are many things you could do.
@AnOminous is correct in all he has stated of course.
I believe advising the DA/Court would be wise. I have a mild concern Nick could get some sympathy from the Judge cause he is such a fucking retard. I hope the judge is purely looking at him as the disgusting stalker/pedo he truly is.
But if it can be made known at the sentencing that he has contacted you, without any doing on your part, it will reflect very badly on him and will show that he does not deserve to see the light of day.
Regardless of what the letter says, sorry, begging, sick shit etc. you don't need the further harm. Its your choice in the end whether you read it or not of course. But the fact that he sent the letter to you knowing full well you want nothing to do with him, shows he does not take your feelings into consideration at all.
What you could do, which I think would be great, and never know Nick might believe it, is go to the post office, say this letter came for the person, but she is deceased. The post office, at least where I live, will stamp the front of the envelope and check off "Deceased" AND RETURN TO SENDER.
In any event, I feel for you being put in this position again. Do what is best for you, and only you. Take care.
I totally agree with Vlad about possibly redirecting any mail you could potentially receive to the address of another Kiwi. You are in contact with Nick which is both a blessing and a curse. If you are not willing to deal with the negatives that come with it then Im sure a Kiwi here would certainly be happy to take this burden off your shoulders.
If you do not wish to post the letter you just received then perhaps you could pass that along to the respective Kiwi.
I thought the same originally. But that would mean pretending to be her wouldn't it? And while the plan is great as we would have a connect to Nick to fuck with him while he is rotting away, it would have to be done as an anonymous troll and not the poor girl who has suffered enough.
So yeah, awesome if it could be done, but have to be a response from Kagney Lynn Moore or something.
tl;dr send the UNOPENED letter to the DA Amber Czerniakowski by whatever means. If the first person even to see it is an officer of the court you can't buy a chain of custody like that and it can be introduced as evidence without any reasonable challenge. It's relevant to his sentencing he's still harassing people even while awaiting sentencing. That shows a total lack of remorse and that he has no ability to stop his criminal behavior.
Another thing in addition to this, is make a request that this be done without it being introduced publicly. Or ask them to admit it under sealed or confidentiality order or something. While doubtful, if the press reports on it, they could mention that Nick sent a letter to the girl he stalked. Once the general troll population sees that, they might start harassing you to find out what the letter said etc.
Again, we all obviously want to see the letter, but not at any further harm to you. Its a shame you were placed in this position by that goof. At least take comfort in knowing he has many tough years ahead of him. I still say (hope) he is dead in 5 or less.