David Katz is one of the best, and most accessible, especially on how the Baltic states have deliberately curated and used it to whitewash their own Nazi pasts and current far-right - mostly because he spent about 25 years living and researching it there (he now lives and teaches in Lithuania).

This a the useful overview article that I posted the other day.

He also collaborated with a number of other academics and historians to create the DefendingHistory website. Here's their archive on double genocide related stuff. There's some background links at the top, then papers by different authors, then related news articles etc.