In the morning hours of July 31, 2014, a former Syrian military police photographer with the code name “Caesar,” sneaked into the U.S. Capitol Complex. Caesar had escaped from Syria with more than 50,000 photos showing mass torture and murder of some 11,000 detainees by Bashar al-Assad’s regime—and was preparing to expose it to the world.

Armed with the photos, Caesar was set to lay bare Syria’s grim reality before the House Foreign Affairs Committee. A congressional staffer who was a former member of the CIA’s clandestine service oversaw the hearing’s security procedures.

GALLERY: Photos of Assad’s Killing Machine (PHOTOS)

But the State Department objected to Caesar, one of the primary witnesses of the Syrian regime’s torture and human rights abuses, speaking publicly before Congress, according to six congressional, State Department, and Syrian opposition sources, as well as contemporaneous documentation.

The State Department said the reason it wanted to downplay the publicity of this hearing was over security concerns, despite elaborate security procedures taken to ensure Caesar’s safety. But several sources familiar with the matter told The Daily Beast that the hesitancy went beyond ordinary security considerations.

“They fought the Caesar hearing tooth and nail. I’ve never seen them fight anything vis-a-vis the committee like that,” said one congressional aide.

A Syrian opposition activist added, “They freaked out.”

This weekend marks the fourth anniversary of an uprising against Syrian President Bashar al-Assad, which sparked the Syrian revolution. Upwards of 220,000 people have been killed in the intervening period.

Caesar’s documentary evidence was, and still is, the most vivid testimony of the human rights abuses that the Assad regime is committing against detainees. In scenes reminiscent of a genocide, Caesar’s photos showed detainees who were killed in a horrific manner: by strangulation, burning, bruising, starvation, and even disembowelment.

Congress is seen as a secure site for many public hearings, featuring high-profile American diplomatic, intelligence and national security officials in open settings on a regular basis. Even the president visits on occasion. Visitors go through magnetometers to access the Capitol Complex for high-profile events, as was the case with Caesar.

The precautions surrounding Caesar’s hearing went even further.

Caesar stayed in an off-the-beaten-path hotel in northeast Washington, D.C. Two nights before the public hearing, they brought him into the hearing room to get him comfortable with the set-up. Late at night, they entered the U.S. Capitol Complex, using a network of underground tunnels to reach the Rayburn House Office Building. They walked through the room and got Caesar comfortable even with the chair he would sit in, before sneaking out of the building after midnight.

On the morning of the hearing, congressional staffers arrived to pick Caesar up from his hotel. En route to his giving his testimony, the staffers employed counter-surveillance techniques to ensure they were not being followed. After these measures were deployed, they drove into a Capitol parking garage.

The former Syrian military police photographer arrived in the Capitol Complex several hours before the hearing, waiting in a well-appointed room in the Rayburn House Office Building, sitting in a plush chair while two men stood guard at the door.

The hearing itself went off without a hitch, but an unusually large number of armed U.S. Capitol policemen were in the room to provide security. And if anyone moved toward Caesar, two Syrian opposition advocates had been tasked with tackling them.

During Caesar’s testimony, he whispered into a translator’s ear with the microphone off, so that that no one could ever hear his voice. And while photographers were allowed access to the meeting at the start, they were asked to leave shortly before the testimony occurred.

Photographers took an iconic photo of Caesar from behind, wrapped in a Blue Patagonia hooded jacket from Hudson Trail Outfitters, talking to members of Congress. To ensure no one could see him, he was also wearing a baseball cap and sunglasses.

After the hearing, Caesar was whisked out of the room by Congressional staff, with the public and media prevented from approaching him. As a further security precaution, a decoy dressed like Caesar left the Capitol—the real Caesar exited in a different disguise several hours later to attend other meetings in Washington, D.C.

These security procedures, in the views of State Department officials at the time, were not sufficient. When Congressional staff laid out the procedures for State Department officials, they simply objected based on vague security concerns. Asked by The Daily Beast, a State Department spokesman declined to elaborate.

Obama administration officials had also tried to dictate to Caesar’s handlers the conditions surrounding his trip to the United States last year. The State Department acknowledges that it wanted “a low-profile press posture for the entire thing, just for his safety.”

The agency insisted that Caesar not be allowed any interviews with news outlets, nor any lawmakers be permitted to issue press releases following meetings with Caesar until he left the country.

A fierce State Department lobbying effort to cancel or at least close the hearing to the public persisted until the night before the committee meeting was to begin. For two days before the hearing, State Department officials called Caesar’s handlers, committee staff, and House leadership nonstop.

The State Department had given special dispensation for Caesar to be allowed into the United States, a process which took months and required extraordinary measures. But the trip had originally thought to include only private, closed-door meetings—and the agency strongly opposed public meetings or press attention.

So, just days before the hearing, the House Foreign Affairs Committee had dropped a bombshell: a hearing with Caesar, open to all.

There was enough mistrust between Congress and the State Department that the House Foreign Affairs Committee’s plans for a hearing were not revealed to the agency until around the time it was announced to the public.

Obama administration officials were taken off guard when they found out, only after Caesar had arrived in the United States, that he would be a witness at an open congressional hearing.

Despite elaborate security precautions that were put in place, the State Department cited security issues: that Caesar’s identity could be inadvertently revealed, or even that he could be assassinated.

“I reject any suggestion that we were less than fully supportive of his visit, his briefings or his meetings,” said a State Department spokesman. “We initiated the process to bring him here so that U.S. government officials who were analyzing some of the evidence he provided, members of Congress and others could hear directly from him about some of the abuses the [Syrian] regime committed.”

Yet the visit also raised uncomfortable questions. Despite the Obama administration’s stated policy of opposing the Assad government, the U.S. hadn’t done much to force him out. In some instances—like the removal of chemical weapons—Washington and Damascus even worked together.

At the time, the Obama administration was sensitive about critiques of its Syria policy. Shortly after the hearing, a bipartisan group of lawmakers met with President Obama at the White House. Responding to the suggestion that he should have armed the Syrian rebels earlier, the president said that criticism was “horseshit.”

Some in Congress believed that this attitude spilled over to Foggy Bottom, and that it made the State Department less than eager to highlight Assad’s atrocities.

“The point was not to hide it under a bush. We were trying to tell the world that this terrible atrocity was happening,” a congressional aide said. “[The Obama administration] didn’t want to answer the question—‘Well, what are you going to do about it?’ It’s a tough question, and they didn’t want that.”

That accusation is a point that prompted aggressive pushback from the State Department.

“The reasons that we urged a closed briefing,” a spokesman said, “was for security reasons only.”