German news are saying today that the German federal attorney general (Generalbundesanwalt), Jens Rommel, has indicted the Ukrainian special forces officer Serhii K. in Hamburg where K. is in custody, for
- attacking civilian energy infrastructure ("a war crime")
- causing an explosion
- destroying a built structure
https://www.tagesschau.de/investigativ/anklage-nordstream-ukraine-russland-100.html
According to the article, the weight of evidence against him is overwhelming. Among other things, he made phone calls while still in Italy (where he was apprehended ast year) that were wiretapped, in which he incriminated himself. Also, his mobile phone is alleged to hold evidence linking him to the attack.
K.'s attorneys have applied for so-called "functional immunity", arguing that the gas pipes were important infrastructure in Russias war and thus a legitimate military target, and K. thus acting as a soldier. This application has been denied - and it, too, appears self-incriminating.
This is the same argument Poland has advanced to explain why they won't extradite a second suspect, a diver named Volodymyr S.
Apparently investigators were able to track the chain of responsibility to "state agancies" ("staatliche Stellen") in Kyiv, with the plot leader being the former Ukrainian secret service officer Roman Tschervinsky, with "insiders" claiming the "go" came from then army chief Valerij Saluschnyj. Whether President Zelenskyi was involved or knew about the plans is unknown.