No extraña que le arrestaron.

English Original Sentence

No wonder he was arrested.

I had expected the subjunctive, arrestaran. :thinking:

The phrase “no wonder…” is like “that explains why…”

So the person being arrested in the sentence was an actual event that was completed, despite the word “wonder”.

I see your point, but I found this thread about no es de extrañar que and choice of mode:

Also, I think one can see this expression as another way to say es lógico que, which does take the subjunctive: