In June, two teams of F.B.I. agents travelled to separate locations in Europe to interview two men who had been prisoners of the Islamic State in Iraq and al-Sham, or ISIS. Both former hostages had been held in northern Syria and were released for reasons that have not been publicly acknowledged. (Some governments have paid ransoms. France, for example, has paid fifty-eight million dollars in ransoms to radical Islamist groups since 2008, according to a recent _Times _investigation. As a matter of policy, the U.S. government does not pay for the release of prisoners.)

The F.B.I. is responsible for investigating crimes against Americans overseas, such as kidnappings and murders. Several Americans have disappeared in Syria since 2012, including the journalists James Foley and Steven Sotloff, each of whom was beheaded on camera recently by a masked militant with a British accent. The agents hoped that the European former hostages could help them find these missing Americans. The agents listened as the former hostages relived their ordeals—recalling where they had been detained and how they had been treated by their captors. They both said that they had been two of several hostages being held at the same site. “It was very, very good intel,” a special-operations officer with intimate knowledge of subsequent events told me.

One of the former hostages described a single-story building where he had been kept in Syria. It was, he said, near a compound and an oil facility outside of Raqqa—a city in northern Syria, which ISIS has taken up as its ad-hoc capital. He recounted what the special-operations officer called the “rhythms of a routine” at the site—daily “patterns” of the captors. In this and other interviews, more details emerged: one of the captors spoke with what sounded like a British accent. (Another former hostage has told the Guardian that three of the guards were born in the United Kingdom and, thus, were called the Beatles.) Foley and Sotloff were being kept in the same place, and, it was said, were subject to frequent beatings. (Another European who was held with Foley and Sotloff, a journalist named Didier François, told the radio station Europe 1 that ISIS’s treatment of Foley was “macabre,” and included mock executions and forcing Foley to stand against a wall to “pose as if he had been crucified.” The Washington Post has reported that Foley and three others were also waterboarded.) The F.B.I. came away with sketched diagrams of the makeshift prison, including the room where prisoners had slept and the guards’ toilet.

The F.B.I. agents relayed this information back to Washington. The National Security Agency, along with other intelligence agencies, tried to identify a building that matched the former hostage’s description. This process took some time, in part because the United States was not employing surveillance drones in Syria. Eventually, a building was pinpointed using satellite surveillance. The special-operations officer conceded that, by this point, the intelligence was “a little bit stale”—the most recently released hostage had been freed weeks earlier—but added, “You couldn’t not take a swing.” The question was whether ISIS had already moved the remaining prisoners to a new secret location: “They must have realized that when they let these guys go, stuff was going to get out. They’re not idiots.”

Anticipating a possible rescue mission, a unit of Delta Force operators left from Fort Bragg, North Carolina, destined for a base in a country neighboring Syria. A geosynchronous satellite monitored the supposed safe house. On July 3rd, a little after 2 A.M. local time, several Black Hawk helicopters left the base, according to the special-operations officer, who asked to remain anonymous because he was not authorized to discuss the operation. Some of the Black Hawks carried Delta Force operators; others were Direct Action Penetrators, or DAPs, which do not carry personnel and are modified with rocket pods, 2.75-inch rockets, and chain guns. All of the aircraft crossed into Syrian airspace and headed toward the site outside of Raqqa.

As the helicopters approached the target, two armed Predator drones joined the operation, circling overhead. (Warplanes were also in the vicinity, “on standby.”) With the DAPs providing cover, the manned helicopters landed and unloaded the team of Delta operators. A gunfight ensued, and two ISIS fighters were killed. The soldiers stormed the apparent safe house, but Foley and Sotloff were nowhere to be found. “It was a dry hole,” the special-operations officer said. The house matched, room for room, the sketches that the F.B.I. had. At one point, a bullet struck one of the helicopter pilots in the leg. The special-operations officer said that the Delta operators were confident that Foley and Sotloff had been there.

The Delta team searched the premises, looking for false walls or other hiding places. While doing so, they grabbed items of potential forensic value: “A couple of phones, blankets—anything that might have hair on it.” (The phones and blankets have been handed over to technicians at an F.B.I. laboratory.) After approximately an hour at the site, the operators re-boarded the Black Hawks, and were back in the “neighboring country” by sunrise. President Barack Obama was kept apprised of the mission by officials in the Situation Room. Among those present were Secretary of State John Kerry and National Security Adviser Susan Rice.

The special-operations officer, who has extensive experience with special-mission units, said that he was generally wary of “hostage scenarios,” because, “once you start chasing that merry-go-round, you’re never going to get off.” He listed other Americans who were thought to be held hostage by various groups around the world; though he was sympathetic to their plight, he didn’t believe that each one warranted a rescue attempt. The bid to free Foley and Sotloff was different: it had a double purpose, he said, “an ability to go get the hostages and also to send a message to ISIS.” (At least two other Americans involved in humanitarian work are being held by ISIS, according to the Washington Post. Last week, ISIS demanded a $6.6 million ransom for one.) After saying this, however, he observed that it might be a folly to treat members of ISIS as rational political actors: “They are lunatics.”

On August 20th, the day after ISIS released a video showing one of its members beheading Foley, Obama said that the world was “appalled” by the gruesome death, and pledged to be “relentless” in pursuing his killers. That evening, Obama’s counterterrorism adviser revealed that a failed rescue mission had taken place.

Two weeks ago, Secretary of Defense Chuck Hagel and General Martin Dempsey, the chairman of the Joint Chiefs of Staff, held a press conference at the Pentagon. When Dempsey was asked whether he thought that Foley had been at the site of the unsuccessful mission, he replied, “I do.” Then he discussed military options for defeating ISIS, which, he said, has an “apocalyptic, end-of-days strategic vision.” The United States has been bombing ISIS in Iraq since early August, and though the group has retreated from the Mosul Dam and Mt. Sinjar, it continues to control vast tracts of land in Syria.

At the press conference, Dempsey said of ISIS members, “Can they be defeated without addressing that part of their organization which resides in Syria? The answer is no.” To defeat them, he went on, the group will “have to be addressed on both sides of what is essentially, at this point, a nonexistent border.” Today, the Web site Bellingcat reported sightings of American drones flying over Raqqa. (A Pentagon official would neither confirm nor deny that drones are now present in Syrian airspace.) The Raqqa raid may have been the first such effort in Syria, but it seems unlikely to be the last.

Further reading:_ _Nicholas Schmidle on the Bin Laden raid; Dexter Filkins on the death of Steven Sotloff; Amy Davidson on Shirley Sotloff's plea to ISIS; and Jon Lee Anderson, George Packer, and Mark Singer on the death of James Foley.