I thought it was interesting that he used the phrase "immediately before the exam". I took that to mean the defense thinks it happened after she left the Duke party. I'm not up to speed on how closely an exam can pinpoint the time of deposit, so I'm just speculating. AFAIK, there's no ATM camera for those kinds of deposits:)
The SANE report may show still "active" sperm were retrieved from who we now know was a single male source. Sperm can live a few hours there:
http://www.goaskalice.columbia.edu/0797.html