I heard this on the Duran podcast, which is a good source of geopolitics from a realist perspective, as they follow official readouts fairly diligently (so I don't have to).
They got this from a German government press conference about the investigation being closed. I emailed them if there is an online link to a transcript (it will be in German, but that's fine). If I get a response, I will update. You can search german transcripts of press conferences from Oct 16-17 on the subject of ending the investigation.
>the Duran podcast, which is a good source of geopolitics from a realist perspective
The Duran is a heavily pro-Kremlin source:
>Founded in 2016, The Duran is a strongly right-leaning news and opinion website with ties to Russian state media. Based in Cyprus, the website’s editor is Alexander Mercouris, who in 2012 was disbarred as an attorney in London. According to the Telegraph, he then went on to become a “pro-Russian commentator on world affairs for Russian TV news outlets and websites.”
>In review, The Duran publishes news and opinions with a conservative and pro-Russian perspective
I can't find any statement of the German government anywhere declaring this "closed", much less that they "know who did it". (It'd also be a pretty weird statement to make, given the Swedes, who are leading the investigation since its their territory, only a few days ago formally confirmed that they could prove that explosives were used)
17th October (EDIT: or the days before, slightly conflicting info) apparently the German ships that took part in the first official inspection came back, but ... that's not "ending the investigation"!
https://www.youtube.com/watch?v=65saUjbbNLM
They got this from a German government press conference about the investigation being closed. I emailed them if there is an online link to a transcript (it will be in German, but that's fine). If I get a response, I will update. You can search german transcripts of press conferences from Oct 16-17 on the subject of ending the investigation.