Beyond Hersh's unnamed source, not that I know of. Again I don't believe it disbelieve it. But I don't dismiss it out of hand because it's not enumerated in an NYT article or a wikipedia page.
1. Stoltenberg didn't get arrested because he was the son of a high-ranking government official.
2. He had a secret history of collaboration with American intelligence going back to his teenage days that is only being mentioned now in a single line in a paragraph with several other factual inaccuracies.