There was a great abundance of material published and distributed throughout the West, but particularly in the United States, about Soviet executions of civilians. This was not limited to just the KGB.

A good couple of primary sources to reference in this matter would be Albert Kalme's Total Terror: an Exposé of Genocide in the Baltics and Juozas Lukša's memoire Forest Brothers: the Account of an Anti-Soviet Lithuanian Freedom Fighter. Both of these works were initially published in the early 1950s and attracted a great deal of attention, especially among Baltic communities in the West. Both of these works also exhibit myriad examples of the atrocities perpetrated by Soviet security forces (Cheka, KGB, &c.).

Similar works documenting atrocities during the time of the Soviet regime after WW2 abound and can be easily found according to the region/ethnicity of their author (e.x. Hungary during the Budapest Uprising in 1956).

As to the response from the West in general, your results will vary depending on the country and the decade. In the United States however, at least in regards to reported atrocities in the Balitcs, the most vigorous reaction predictably came from Baltic communities. From my limited research in this regard, I would conclude the reaction from those outside the communities with ties to those being harmed as being more of accepting a matter of fact than outright outrage.

In fine, the information existed and was distributed widely throughout the West. As to how people reacted to that information, it was dependent on the time and place, but most often the most outrage came from those communities with cultural ties with the people being oppressed and executed by the Soviet authorities.

Hope that helps answer your question!

Edit: minor spelling errors