2 separate issues here as I see it.
1. Should aircrew be screened? (Done to death here & elsewhere)
2. A person tested positive to a screening criteria, didn't stick around & was allowed to continue.
I think the real issue for this thread is that a person, who happened to be crew, didn't wait for test results (are they supposed to?) and that the security staff did not act upon this fact. As a professional, and in the interests of teamwork, I think he should have stuck around and, as professionals & in the interests of security, I think the security staff should have acted properly and alerted the authorities of a breach.
On a side note and whilst this screening continues, I personally think aircrew should take the high ground & act as professionals when screened. Maintain the high ground & then the nasty little nazi's that levitate to these types of roles can be found out and seen for what they are worth. I also agree with Tester Call who suggested that the ASIC should be sufficient when passing through a screening area. Having been subjected to the same scrutiny when passing through INTL security, but also having had the option to say "Sod it, I'll go through the canteen or Customs downstairs", it beggars belief that all the other authorities at the airport are quite happy for me to go that way with my ASIC.