I once read a detailed account of how he was caught. It seemed like the kind of clues that you could only connect post-hoc.

It seemed like parallel construction [1] to me. Considering that the NSA is known to give the DEA "tips" [2], and has a division specifically to start parallel construction investigations [3], and this was a high profile drug case, it would be odd that they didn't use parallel construction techniques.

[1] https://en.wikipedia.org/wiki/Parallel_construction

[2] https://arstechnica.com/tech-policy/2013/08/us-drug-agency-g...

[3] https://www.reuters.com/article/world/exclusive-u-s-directs-...