The police report had three screenshots of Hacker News discussions where he had participated. His nickname was redacted (like were all others), but the screenshots are for:
https://news.ycombinator.com/item?id=17696035
https://news.ycombinator.com/item?id=15729517
https://news.ycombinator.com/item?id=25529743
Source: Keskusrikospoliisi / National Bureau of Investigation