While details on the administration’s target-selection program remain patchy, the political imperatives that make it tick are clear enough. The same reasons the Obama administration prefers drone strikes in undeclared war zones to controversial special-forces operations — or to the slow and uncertain progress of aid or police work — also lead it to rely very heavily on signals intelligence, or sigint.

Sigint must appear to the administration to be national security on the cheap — if not financially, then in every other sense. The surveillance web’s perceived human and political cost (until the system was exposed) was minimal. Placing agents in terrorist organizations takes time and is fraught with peril — as the devastating attack at the Khost CIA station in 2009 would have taught the administration. (At Khost, a man the CIA believed to be their agent blew himself up at a meeting with his handlers, causing the greatest loss of CIA lives in over 25 years.) One can imagine Obama musing in the wake of such an attack, “Why not just listen to the terrorists when they speak among themselves?”

Well, for one, humans tend to misinterpret data. The former drone operator presses this point the Intercept: “There is a saying at the NSA, ‘Sigint never lies.’ It may be true that sigint never lies, but it’s subject to human error.”

For a host of reasons, a glossy computer report often masks a very different reality. Anyone who has ever opened a disappointing online purchase — or gone on a disappointing online date — has experienced this in a trivial way. Nor is this problem limited to sigint. Hundreds of hours that I’ve spent poring over human intelligence (humint) reporting in litigation involving Guantanamo detainees taught me the disturbing tendency of computerized intelligence dissemination to mask bias and error — and for mistakes, once recorded, to spread like viruses through any intelligence database. Former intelligence professionals have underscored this problem, saying that it grew worse after 9/11. A piece of misinformation would be excerpted again and again in reports, often stripped of crucial context that would paint the information in an entirely different light.

Meanwhile, the United States’ humint networks in, say, Yemen and Somalia are thin; we apparently have Saudi and U.K. spy work to thank for the seizure of the 2012 underwear-bomb prototype, for example. Misreading of activity-based intelligence is the likeliest explanation for most civilian drone deaths. Again, this is not to say other forms of intelligence are faultless. What happened at Khost is a gruesome testament to that, and what's more, profit-seeking sources have offered false humint that sent many prisoners I represent to Guantanamo Bay. Unreliable sources in the Yemeni security establishment may well have caused innocent drone deaths too.