Imo those tweets absolutely could be interpreted as immediate threat, especially considering what happened in Germany 2 days ago. Also, there is no apology, he just deleted his account. Maybe he went into hiding, who knows what he is going to do, he doesn't seem that stable.
This probably deserves the attention of the police, here is their website / twitter account:
www.poliisi.fi
The latest Tweets from Suomen poliisi (@SuomenPoliisi). Suomen poliisin virallinen Twitter-tili. Finska polisens officiella Twitterkonto. The Official Twitter account of the Finnish Police. https://t.co/PgpEEhT2wS. Finland
twitter.com
Let them deal with this, that's why they exist. Better safe than sorry.