That is a lonely life you live there. Most of your own countrymen hate you, and you pass your time investigating and reporting peaceful dissenters to foreign enemy governments. If there were ever a dictionary definition of the word "pathetic"...

he would be questioned and detained for conspiracy.

And the conspiracy is... not signing a petition? Think about that.

I wouldn't try to ruin his life, only to protect the Russian federation from any domestic threats.

For your own sake, just realise that OP is not the only one who can be de-anonymised, and your own US government doesn't take too kindly to Russian collaborationists at present. I suspect that would be very interested in someone like you found to be reporting Russian dissenters to their government. Like I said in my first comment, threats like yours are a great way attract the wrong kind of attention on the Internet.