The pattern has become familiar: Customs officers wave in vehicles filled with illegal immigrants, drugs or other contraband. A Border Patrol agent acts as a scout for smugglers. Trusted officers fall prey to temptation and begin taking bribes.
HSA is greatly increasing the size of their internal affairs unit as high profile busts of corrupt border and customs guards continue.
Most troubling for them is that some corrupt guards were allied with smugglers before taking their jobs. And of course, some of them could conceivably now be in internal affairs too.
I read somewhere that the Great Wall of China was breached not by force, but by bribing the guards, a time-honored (and highly effective) method indeed.