We are not told very precisely what Chin did for the CIA, but it is clear that he was in a position to see, and "borrow," many highly classified documents. He turned copies of these over to couriers near the Toronto airport, and was paid for them in the course of separate trips that he made
from time to time to Hong Kong.
Eventually the payments Chin was receiving from Peking grew so large that it became necessary to explain to his American friends how a middle-ranking CIA employee was able to invest in real estate all around the Washington area while simultaneously putting his children through school. Chin boasted that he had invented a "system" for winning at Las Vegas and attributed his prosperity to that.
Chin may not actually have had a system for beating the bank in Las Vegas, but he certainly seems to have had one for beating the polygraph in Langley.
All CIA employees are routinely required to undergo lie detector tests at regular intervals, and Chin was surely no exception. How, then, did he manage to fool the machine again and again, over a matter of decades? An honest answer to that question might well be the most useful information Larry Chin has to bargain with, if he's interested in getting his prison term shortened a bit. Secretary of State Shultz's well-known reservations about such tests simply increase the question's urgency.
Polygraphs, better known as "lie detector machines," aren't perfect, and are not ordinarily accepted as valid sources of evidence in court. But they do measure the subtle physical indications of stress that are produced by (among other things) the effort of lying. They can, therefore, be extremely useful in spotting sensitive areas in the course of a long series of questions, and in a setting like Langley they have, to my personal knowledge, resulted in discoveries extremely useful to those concerned with American security.
There are all sorts of old wives' tales about how to beat the polygraph - e.g., to disrupt reaction patterns by hiding a pebble between your toes and squeezing it (to produce pain and a blip on the machine) at irrelevant moments. But Chin must have confronted the monster dozens of times, and seems to have fooled it every time. Is he some sort of pathological liar, from whom lying elicits no more effort, let alone stress, than telling the truth? Or is he somehow particularly nerveless and low-key, in a way that simply anesthetized the machine?
Whatever the explanation, it seems likely to lead to revisions in the CIA's already strict procedures for granting and renewing security clearances. And if any part of Larry Chin's explanation can be made public in due course, without damage to national security, I hope the CIA won't allow its natural penchant for secrecy to deter it from releasing it. The human race in general has a legitimate interest in knowing just how fallible these lie detectors can be.