A polygraph can be junk if it's used improperly. I do think though, that if administered properly, they can be helpful. Early on in this investigation several FBI agents, (former), gave pretty good details on how an effective polygraph would be administered. Starting with basic questions, leading into more detailed questions and finally with very specific questions. Throwing in a question occasionally with details that were not public. That only the guilty party could possibly know. Otherwise, they could react just based on things they had heard/read.
As far as when Billy Martin said this, it was on LKL last night. He was interviewed along with Chandra's aunt, Linda Zamsky and another woman that is a Levy family spokesperson. I can't remember her name right now, but the entire transcript is on cnn.com
Last night, huh. Can't get much more recent than that. That is a very interesting thing for him to have said.