I'm not stating it is perfect, I'm just trying to give people some insight into the process.
A serial killer to-be gets through the poly.
You are comparing apples to oranges. The actual polygraph only ask yes and no questions. The packet of information you must complete before the poly only ask "have you ever... " type of questions. An employee becoming a future serial killer would have to be discovered during a psychological evaluation, not a polygraph. I don't know if DHS requires a pre-employment psychological evaluation or not??
ole devil dog up there with a TSSCI gets dq'd
Again, each agency sets the standard for it's "Qualification Review" for employment. I don't know the circumstances for the former Marine, but the standards for a DOD clearance may be different from DHS Law Enforcement TS clearance. Does the former marine have a medical condition that indicates a false positive on a poly??? Possibly....
It's not a perfect system. The Agency I work for requires a polygraph as well as other series of events for all Law Enforcement certified employees. I can tell you that over 90% of applicants either fail an assessment or drop out along the way. So if we are trying to run a new hire class of 20, we must start with over 200 applications.
Again, I'm not trying to defend the DHS polygraph. All you can do is apply and go through the process. I'm just trying to help explain the process.