BHO and drug test

Greetings,

I am an attorney. I have a client who has been smoking honey oil on a regular basis for some time. He was recently placed on probation and has been testing positive for THC for what he claims is his past use of BHO. I am trying to find information to support the proposition that THC from BHO will stay in your system (urine) for a longer period of time than it would from marijuana. It makes sense on a logical level - higher concentrate of THC = higher volume in your system - but sometimes logic and the law (prosecutors/probation officers/judges) don't go hand in hand. Can anyone help me out. I'm not really looking for past experiences so much as I am looking for a scientific/pharmacological explanation as to why it would stay in your system longer. Thanks.