As Alec Leamas said in the film version of The Spy Who Came In From The Cold, "It's the innocents who get slaughtered." Similarly, Joseph Brodsky says that "the chorus," perishes. The following examples prove that the victims in the novel were not directly involved in the affairs of the spies, but were innocent.
Elvira, Karl Reimeck's mistress, is a perfect example of an innocent bystander turned victim. While Riemeck was alive, he spent a lot of time with Elvira. During those times with her, he confided in her; he told her things about his "business" that she should have never known. Because his associates discovered Riemeck had let his mouth slip, they were forced to murder both Riemeck and Elvira -- for fear that both might not keep their mouths shut. Just because this woman knew some things that she probably didn't want to even know, she had to die.
Liz was also an innocent character who was unknowingly involved with the "spy business." From the beginning, the whole operation was planned out. Leamas would take the job at the library and meet Liz and, in turn, have a relationship with her. With Liz in the plot, she could testify at the Tribunal. Her testimonial would prove that Leamas was out to kill Mundt and the latter was never affiliated with the British. Without her knowledge, she saved Mundt's life. That is why it is such a shame that she was killed at the end of the story; she was innocent.
Another example of innocence in The Spy Who Came In From The Cold is Fiedler. The only thing he set out to do was frame Mundt. He came very close to doing so too. If it was not for Liz and her testimony, Mundt would have been dead and Fiedler would have proved his case against the man - that Mundt was secretly working for the British. Much like Elvira and Liz, innocent Fiedler was put to death - for doing his job, of all things!.
Many times in life we experience pain and suffering for no apparent reason.