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.
This isn't entirely true. The work camps were powered by convicts, but also by putatively free exiles who had been sent there for a variety of reasons. And in some cases, convicts who had completed their sentences were technically freed, but not allowed to leave the camps anyway.
Source: I'm currently reading "Gulag: A History" by Anne Applebaum. https://www.goodreads.com/book/show/224379.Gulag
Others have pointed this out, but penal servitude is alive and well in the US prison system as well [1] and it's not common to use the word slavery for that. Maybe they should, but it is arguably a different concept from chattel slavery.
[1] http://en.wikipedia.org/wiki/Penal_labor_in_the_United_State...
http://en.wikipedia.org/wiki/Penal_labor_in_the_United_State...
The point is there is a spectrum/grey line.
[0] See, e.g., US Constitution, Amendment XIII