BROWNSVILLE, Texas — When a regional manager for the Mexican Gulf cartel moved his operation to a more lucrative territory on the border, he took along not only his armored trucks and personal army, but also his department heads and a team of accountants.

It's easy to lose sight of the fact that, ultimately, these criminal organizations are complex businesses, relying on careful accounting as much as assault rifles.

Rafael Cardenas Vela testified this week about the organization's structure and operations in such detail that it could compose a short course — Narco 101, perhaps.

The U.S. Border Patrol sector that covers much of the Gulf cartel's territory seized just over 1 million pounds of marijuana in 2011 and apprehended nearly 60,000 illegal immigrants.