Not for the first time, the most compelling piece of information in an investigation is what isn’t there.

We’ve written often before about the failure of databases and artificial intelligence to knit together output from various databases and I discussed the idea of what isn’t there in my book, The Art of Fact Investigation. Remember, two of the biggest red flags for those suspicious of Bernard Madoff were the absence of a Big Four auditor for a fund the size he claimed to have, as well as the absence of an independent custodian.

The most famous example of missing evidence is from Sherlock Holmes: the dog that didn’t bark when the horse was removed from its stall during the night. No barking meant the dog knew the person who took the horse. It’s discussed by an evidence professor here.

This week, another excellent example: The Center for Advanced Defense Studies (C4ADS) provided an advance copy of its report to the New York Times and Wall Street Journal, detailing the way Kim Jong Un evades international sanctions. The report, Lux & Loaded is an example of superior investigation.

Using public records that track ship movements, commercial databases that record the movement of goods, and publicly available photos on the internet, C4ADS makes the case that Kim was able to get his hands on two armored Mercedes-Maybach S600 cars worth more than $500,000 each.

The report details the movement of the cars from a port in the Netherlands through several transshipment points, but the key finding is that the ship last seen with the cars “vanished” for 17 days last October, while the cars were in transit off the coast of Korea. While unable to say conclusively that the cars moved from Rotterdam to North Korea, the evidence is persuasive.

Most interesting is not the evidence that they could not find because it does not exist in open sources, but the evidence that was removed because a Togo-flagged ship called DN5505 turned off its transponders. It’s as if the ship just disappeared from the high seas.

Maybe we should not expect to be able to track every cargo shipment in the world every moment it’s at sea, but ships going dark for weeks at a time is something that should arouse suspicions.

That’s why, among the organization’s recommendations is that insurance companies should require that ships keep their transponders on in order to acquire and maintain insurance.

That won’t catch sanctions busters every time, but it’s a very sensible start.