Probably because they were technically convicts from governments point of view, instead of outright slaves or someones property.

I'm a bit surprised by 1954 as the date, since it's pretty far from the original purges in the 30s, but not at all surprised by the find. The disappearances and summary judgements, resulting in either executions or the slow rot of the labor camps, are well documented.

A person I know from that same town found a German gun folded in oiled cloth in his parents' ceiling when he was renovating. The building was built by German POWs.