Soviet secret police
The Soviet Secret Police are known in the West by abbreviations. They commenced with the Cheka, the GPU, the NKVD, the OGPU, the MGB, the GUGB, the NKGB, the MVD, and the KGB.
For most agencies, secret policing operations were only part of their function. For example, the KGB was both the secret police and the intelligence agency.
They were major parts of the mass killings under Communist regimes.
Regarding Jewish influence, see Jews and Communism, the section on "Russia" in Jewish influence and the "External links" here. Jewish influence, at least regarding the highest positions, was reduced during the Great Purge.