The human question is: why?
Investigators have been explicit about the limits of what they know. There was no arrest warrant for Robert Nichols when he disappeared in 1964. Investigators have said this clearly, eliminating the most obvious possible explanation: he was not, as far as anyone can determine, running from law enforcement. There is no established connection to organized crime. There is no established debt or financial crisis that has been documented as a driver of his departure.
The departure itself was not spontaneous. He filed for divorce before leaving. He told his wife she would learn his reasons in due time. These are the actions of someone who had made a decision and was implementing it, not someone who fled in panic. Whatever drove him away from his family was something he had considered enough to act on deliberately, to explain partially (“you’ll understand in due time”), and to execute in stages over what appears to have been several months.
The thirteen years during which he apparently continued to exist under his real name — paying taxes, receiving wages — suggest that the initial departure was not necessarily the same impulse that eventually drove him to assume a false identity. He disappeared from his family in 1965 without necessarily disappearing from the world. Something in the subsequent decade — something between approximately 1976 and 1978 — escalated whatever the original situation was, or created a new situation, sufficient to drive him to formally erase his identity.
The phrase “they’re getting close,” repeated over years to co-workers, implies an awareness of being tracked or monitored — a belief, accurate or not, that someone was looking for him. The packed suitcase implies sustained readiness to flee. The disappearances from his apartment and workplace, lasting days or weeks, suggest either that he did flee on some occasions — that “they” came close enough that he felt he needed to move — or that his anxiety periodically overwhelmed his ability to maintain his routines.