Final answer:
The sentence implies that all deaths had the same cause affecting everyone indiscriminately, symbolized by an omnipresent ‘invisible stalker’ moving through the streets.
Step-by-step explanation:
The sentence 'No one knew that a killer was already moving through their streets with them, an invisible stalker that would go house to house until it had touched everyone, rich or poor, in some terrible way' suggests that all the deaths had the same cause, and everyone would be affected. This option underscores the universal and indiscriminate impact of the threat, implying that it acts without regard to wealth or status and painting a vivid picture of an unseen but pervasive danger. It conveys a sense of inevitable and indiscriminate reach, as nobody, regardless of their station in life, would remain untouched by this 'invisible stalker'.