When the Red Army overtook groups of people, what happened to them? The "death march" narrative encompasses groups fleeing to avoid being trapped in Soviet territory after the war ended. They could deported to camps, shot as collaborators/traitors, imprisoned, interrogated, put on trial in the USSR, etc.
This Russian book is titled Special camps of the NKVD / Ministry of Internal Affairs of the USSR in Germany. 1945-1950.
Going through some of the documents with AI translation, there's a lot of material on how the Iron Curtain closed around groups of people at the end of the war, and the burgeoning NKVD camps.
Whether people "death marched" back to Germany or not, the USSR would scoop them up, imprison them, and send them to camps.
Here's excerpts from one short document:
Post-war Polish camps could also be discussed here. Jews came back to Poland from the Soviet Union with Polonized names and had an outsized influence in these camps. They changed their names at the insistence of the Comintern, according to at least one source I found.Of the total number of those seized, Germans accounted for 138,200 people, Poles - 38,660 people, Hungarians - 3,200 people, Slovaks - 100 people, Italians - 390 people, and citizens of the Soviet Union (Russians, Ukrainians, Belarusians, Lithuanians, Latvians, Kazakhs and others) - 27,880 people.
Of the total number of 215,540 people seized, 148,540 were sent to NKVD camps, 62,000 are in front-line prisons and NKVD camps, and 5,000 died during the operation and en route to the camps.
[...]
It should be noted that of those arrested for detention in NKVD camps, no more than half of the total number can be used for physical labor, since the rest are old people and people unfit for physical labor.
[...]
1. Henceforth, as the Red Army advances through German territory, when carrying out measures to clear the rear of active units of the Red Army, limit yourself to the removal of persons of the following categories:
[...]
2. Cease the transfer to the USSR of persons arrested during the clearing of the rear areas of active Red Army units, organizing the necessary number of prisons and camps for their detention on site. Transfer to the USSR only those arrested who are of operational interest.
Report of the People's Commissar of Internal Affairs of the USSR L.P. Beria to the Chairman of the State Defense Committee I.V. Stalin on the work to clear the front-line rear of the active Red Army by units of the NKVD of the USSR, on the composition of those arrested by category, on amending the NKVD order No. 0016 of January 11, 1945. April 17, 1945
Source