Strozk didn’t have a security clearance while he was doing many of his evil deeds. That is because he failed his Poly. He was given a security clearance retroactively (don’t know how that is possible). Most likely so all the people that gave him classified info didn’t go down with him. Probably many were underlings that didn’t know. He was most likely escorted out for multiple reasons, one of which was that most likely his clearance was stripped.
Polygraph is a tool in doing initial clearances and evaluating employees of various departments at regular intervals. The rules for DOD, DOJ and say, NASA are not totally uniform for employment purposes however there are standards for certain programs such as SAP.
Having built SAPF areas for DOD branches prior to retirement I got a general impression of the clearance processes from off hand impressions. Many people "fail" or don't have a "clear" polygraph and interviews and fine tuning generally make "Passing" a polygraph not a yea or nay thing in determining if a person gets various levels of security clearance.