Anouschka and I stood in the parking lot of an empty gas station, leaning against the hood of the rental car. It was hot. In southern Spain, it’s always hot. The gas station sat at the base of a curving canyon road; high walls of red rock rose on either side of us, meeting the impossibly blue sky overhead. I listened to Anouschka, my translator, chatter on the cell phone in Spanish. She finished her conversation and snapped the phone shut. “José is coming down to meet us,” she said. “He says we’ll recognize him because he looks like an ugly Hugh Laurie.”

She paused. “Hugh Laurie is already pretty ugly, no?”

I had come to the Spanish desert in the winter of 2007 to research a book about a cold war nuclear accident. On January 17, 1966, an American B-52 bomber carrying four hydrogen bombs collided with a tanker plane during a mid-air refueling over Spain. Both planes exploded, killing seven airmen and launching the four H-bombs into the sky. Three bombs landed around the small farming village of Palomares. There was no nuclear explosion, but the impact detonated the high explosive in two of the bombs, spreading plutonium for miles. The bombs were quickly recovered, but cleanup of debris and contaminated soil took months. The fourth bomb landed in the Mediterranean, and it took nearly three months—and the largest salvage effort in Navy history—to recover it. The broken arrow at Palomares is still regarded as the worst known nuclear weapons accident in all history, and the American cleanup remains the subject of considerable controversy in Spain. José Herrera Plaza, an eccentric documentary filmmaker (and Hugh Laurie look-alike) who was coming down the canyon to meet us, was my last chance to find out what exactly had happened in that patch of Spanish desert.

Why was this the case? Why was I, an American journalist, unable to get information about a forty-year-old, publicly acknowledged nuclear accident? The answer is a mixture of politics and bureaucracy, one reporter’s quixotic battle against the nearly impenetrable edifice that is the U.S. Department of Energy.

In 2004, I began gathering information for my book about the Palomares accident. One of my goals was to discern the extent of plutonium contamination in Spain and determine if the Spanish or American governments had intentionally concealed its magnitude. I knew this much: after the accident, the United States Air Force made a massive effort to clean up the plutonium, agreeing to remove the most contaminated topsoil and vegetation. For weeks, airmen loaded contaminated dirt and tomato vines into steel drums. In March 1966, they put 4,810 of these barrels onto a Navy ship and sent them to the Savannah River facility, a plutonium plant and nuclear fuel disposal site in South Carolina, for burial. The United States also helped establish a long-term health monitoring system for the people of Palomares. With these measures completed, most people considered the matter closed.

Unfortunately, the cleanup was incomplete. The most contaminated site, called area #2 because the Americans found the second bomb there, was a steep and rocky stretch on the far outskirts of town. Rather than remove topsoil from area #2, the Air Force—after sometimes tense negotiations with the Spanish government—agreed to turn the dirt with picks and shovels, diluting the plutonium until the radiation count dropped below the level of detection. This left a large swath of Spanish countryside contaminated. El País, the largest daily newspaper in Spain, also reported that the Americans had left behind two buried trenches, about ten yards wide and thirty yards long, containing radioactive debris. Area #2 and the mysterious trenches became focal points of my research. How bad was the contamination? How long had the authorities known about the buried debris? Had there been a cover-up?

Before my trip to Spain, getting information in the U.S. had proven exasperating. I wasn’t alone. Many historians, especially those researching nuclear weapons, were frustrated as they tried to access documents during the Bush administration years. An August 2006 article in The Washington Post, for example, described how researchers at the National Security Archive, an independent research institute located at George Washington University, were surprised to find cold war statistics on the number of American nuclear weapons blacked out in documents they had obtained. This was curious because the numbers had been published in the past, and more detailed ones had been given to the Soviets during arms control talks. The DOE was known for its openness during the Clinton years, but after 9/11, the Bush administration initiated a massive reclassification campaign, squirreling away documents that had long been public. My research was caught up in the sweep.

Barbara Moran is a science journalist in Boston. Her first book, The Day We Lost the H-Bomb: Cold War, Hot Nukes, and the Worst Nuclear Weapons Disaster in History, was published by Presidio Press, an imprint of Random House, in 2009.