I do believe the lie detector test is more accurate than 50/50.
No properly-conducted scientific study has ever come up with results better than 60%, and that only happened once (so it may have just been a fluke). Most scientific studies have concluded that the machines are accurate at only 50%.
Two separate governmental advisory boards have investigated polygraph machines and concluded that they are not reliable enough to be trusted. There are dead US agents who would be alive if the CIA hadn't trusted polygraph machines. The terrorist who mailed anthrax to people in 2001 passed two polygraph tests.
To the best of my knowledge, and I have looked, there is no
scientifically-valid evidence that polygraph machines work much better than random chance. None. So why would you believe in them?
In a post about astrology and tarot cards, I said that it's not enough to be honest and say what you really believe: you also have to test what you believe to see if it's really true. Polygraph machines have failed every time they've been put to a scientifically-rigorous test.
I'm sorry for your pain. I truly am. Some days I read the posts on this site and I feel totally powerless. I was supposed to get wise when I got old, but people here ask questions I have no answers for at all.
And I really wish there was some way you could get the truth once and for all and be settled in your mind. But as of right now, there just isn't a technological solution for you, any more than there's a car that gets 500mpg. Maybe one day, but not yet.