This is a big ask since the number of people in terms of perpetrators and bystanders is rather large. A good place to start is Yitzhak Arad’s Belzec, Sobibor, Treblinka, which is still among the best secondary sources on Aktion Reinhard.

Go from Arad’s sources as a starting point. In addition, you’ll want to look into the West German trials for these camps, which were held in the 1960s. German trial transcripts are generally not complete, but the Institut für Zeitgeschichte in Munich has many of the affidavits on which the trial testimony was based. A lot of these documents have been scanned and can be read online, so if you can read German, you’ll find them useful.

Finally, very much worth consulting is Claude Lanzmann’s film Shoah, which contains multiple testimonies from survivors and perpetrators both. At nine hours long, it is a bit of a slog, but not all of it specifically deals with Aktion Reinhard. It has the secretly taped testimony of Franz Suchomel, an SS soldier assigned to Treblinka, which provides one of the best available testimonies of conditions in that camp.

It is unlikely you will get all the testimony this way, but you’ll have virtually all the survivor testimony and much of the perpetrator and bystander testimony.