On Feb. 12, 2008, Imad Mughniyah, Hezbollah’s international operations chief, walked on a quiet nighttime street in Damascus after dinner at a nearby restaurant. Not far away, a team of CIA spotters in the Syrian capital was tracking his movements.

As Mughniyah approached a parked SUV, a bomb planted in a spare tire on the back of the vehicle exploded, sending a burst of shrapnel across a tight radius. He was killed instantly.

The device was triggered remotely from Tel Aviv by agents with Mossad, the Israeli foreign intelligence service, who were in communication with the operatives on the ground in Damascus.

“The way it was set up, the US could object and call it off, but it could not execute,” said a former US intelligence official. The United States helped build the bomb, the former official said, and tested it repeatedly at a CIA facility in North Carolina to ensure the potential blast area was contained and would not result in collateral damage.

“We probably blew up 25 bombs to make sure we got it right,” the former official said.

The extraordinarily close cooperation between the US and Israeli intelligence services suggested the importance of the target—a man who over the years had been implicated in some of Hezbollah’s most spectacular terrorist attacks, including those against the US Embassy in Beirut and the Israeli Embassy in Argentina.

The United States has never acknowledged participation in the killing of Mughniyah, which Hezbollah blamed on Israel. Until now, there has been little detail about the joint operation by the CIA and Mossad to kill him, how the car bombing was planned or the exact US role. With the exception of the 2011 killing of Osama bin Laden, the mission marked one of the most high-risk covert actions by the United States in recent years.

US involvement in the killing, which was confirmed by five former US intelligence officials, also pushed American legal boundaries.

Mughniyah was targeted in a country where the United States was not at war. Moreover, he was killed in a car bombing, a technique that some legal scholars see as a violation of international laws that proscribe “killing by perfidy”—using treacherous means to kill or wound an enemy.

“It is a killing method used by terrorists and gangsters,” said Mary Ellen O’Connell, a professor of international law at the University of Notre Dame. “It violates one of the oldest battlefield rules.”

Former US officials, all of whom spoke on the condition of anonymity to discuss the operation, asserted that Mughniyah, although based in Syria, was directly connected to the arming and training of Shiite militias in Iraq that were targeting US forces. There was little debate inside the Bush administration over the use of a car bomb instead of other means.

“Remember, they were carrying out suicide bombings and IED attacks,” said one official, referring to Hezbollah operations in Iraq.

The authority to kill Mughniyah required a presidential finding by President George W. Bush. The attorney general, the director of national intelligence, the national security adviser, and the Office of Legal Counsel at the Justice Department all signed off on the operation, one former intelligence official said.

The former official said getting the authority to kill Mughniyah was a “rigorous and tedious” process. “What we had to show was he was a continuing threat to Americans,” the official said, noting that Mughniyah had a long history of targeting Americans dating back to his role in planning the 1983 bombing of the US Embassy in Beirut. “The decision was we had to have absolute confirmation that it was self-defense,” the official said.

There has long been suspicion about US involvement in the killing of Mughniyah. In The Good Spy, a book about longtime CIA officer Robert Ames, author Kai Bird cites one former intelligence official as saying the operation was “primarily controlled by Langley” and it was “a CIA ‘black-ops’ team that carried out the assassination.”

In a new book, The Perfect Kill: 21 Laws for Assassins, former CIA officer Robert B. Baer writes how he had considered assassinating Mughniyah but apparently never got the opportunity. He notes, however, that CIA “censors”—the agency’s Publications Review Board—screened his book and “I’ve unfortunately been unable to write about the true set-piece plot against” Mughniyah.

The CIA declined to comment.

“We have nothing to add at this time,” said Mark Regev, chief spokesman for the prime minister of Israel.

A theory of self-defense

The operation in Damascus highlighted a philosophical evolution within the American intelligence services that followed the Sept. 11, 2001, attacks. Before then, the US government often took a dim view of Israeli assassination operations, highlighted by the American condemnation of Israel’s botched attempt in 1997 to poison the leader of Hamas, Khaled Meshal, in Amman, Jordan. The episode ended with Mossad agents captured and the Clinton administration forcing Israel to provide the antidote that saved Meshal’s life.

The Mughniyah killing, carried out more than a decade later, suggested such American hesitation had faded as the CIA stretched its lethal reach well beyond defined war zones and the ungoverned spaces of Pakistan, Yemen, and Somalia, where the agency or the military have deployed drones against al-Qaeda and its allies.

A former US official said the Bush administration relied on a theory of national self-defense to kill Mughniyah, claiming he was a lawful target because he was actively plotting against the United States or its forces in Iraq, making him a continued and imminent threat who could not be captured. Such a legal rationale would have allowed the CIA to avoid violating the 1981 blanket ban on assassinations in Executive Order 12333. The order does not define assassination.

In sanctioning a 2011 operation to kill Anwar al-Awlaki, a US citizen and an influential propaganda leader for al-Qaeda’s affiliate in Yemen, the Justice Department made a similar argument. Noting that al-Qaeda in the Arabian Peninsula had targeted US commercial aircraft and asserting that Awlaki had an operational role in the group, government lawyers said he was a continued and imminent threat and could not feasibly be captured.

“It’s fairly clear that the government has at least some authority to use lethal force in self-defense even outside the context of ongoing armed conflict,” said Stephen I. Vladeck, a professor of law at American University’s Washington College of Law. “The million-dollar question is whether the facts actually support a determination that such force was necessary and appropriate in each case.”

The CIA and Mossad worked together to monitor Mughniyah in Damascus for months prior to the killing and to determine where the bomb should be planted, according to the former officials.

In the leadup to the operation, US intelligence officials had assured lawmakers in a classified briefing that there would be no collateral damage, former officials said.

Implicated in multiple cases

At the time of his death, Mughniyah had been implicated in the killing of hundreds of Americans, stretching back to the embassy bombing in Beirut that killed 63 people, including eight CIA officers. Hezbollah, supported by Iran, was involved in a long-running shadow war with Israel and its principal backer, the United States.

The embassy bombing placed Hezbollah squarely in the sights of the CIA, a focus that, in some respects, foreshadowed the targeting of Mughniyah. In his 1987 book, Veil, Washington Post journalist Bob Woodward reported that CIA Director William Casey encouraged the Saudis to sponsor an attempt to kill a Hezbollah leader. The 1985 attempt on the life of Mohammed Hussein Fadlallah with a car bomb failed, but killed 80 people, and he fled to Iran. Mughniyah’s brother was among those killed.

Former agency officials said Mughniyah was involved in the 1984 kidnapping and torture of the CIA’s station chief in Lebanon, William F. Buckley. The officials said Mughniyah arranged for videotapes of the brutal interrogation sessions of Buckley to be sent to the agency. Buckley was later killed.

Mughniyah was indicted in US federal court in the 1985 hijacking of TWA Flight 847 shortly after it took off from Athens and the slaying of US Navy diver Robert Stethem, a passenger on the plane. Mughniyah was placed on the FBI’s Most Wanted Terrorists list with a $5 million reward offered for information leading to his arrest and conviction.

He was also suspected of involvement by US intelligence and law enforcement officials in the planning of the 1996 Khobar Towers bombing in Saudi Arabia that killed 19 US servicemen.

For the Israelis, among numerous attacks, he was involved in the 1992 suicide bombing of the Israeli Embassy in Buenos Aires that killed four Israeli civilians and 25 Argentinians, and the 1994 attack on a Jewish community center in the city that killed 85 people.

“Mughniyah and his group were responsible for the deaths of many Americans,” said James Bernazzani, who was chief of the FBI’s Hezbollah unit in the late 1990s and later the deputy director for law enforcement at the CIA’s Counterterrorism Center.

The Bush administration regarded Hezbollah—Mughniyah, in particular—as a threat to the United States. In 2008, several months after he was killed, Michael Chertoff, then secretary of homeland security, said Hezbollah was a threat to national security. “To be honest, they make al-Qaeda look like a minor league team,” he said.

Beginning in 2003, Hezbollah, with the assistance of Iran, began to train and arm Shiite militant groups in Iraq, which later began attacking coalition forces, according to Matthew Levitt, who recently wrote a book about Hezbollah and is director of the Washington Institute’s Stein Program on Counterterrorism and Intelligence.

The Hezbollah-trained militias proved to be a deadly enemy, wounding or killing hundreds of American troops. As the situation in Iraq deteriorated and coalition casualties spiked in 2006, the United States decided it had to stanch the losses.

The Bush administration issued orders to kill or capture Iranian operatives targeting American troops and attempting to destabilize Iraq. It also approved a list of operations directed at Hezbollah, officials said. The mandate applied directly to the group’s notorious international operations chief.

“There was an open license to find, fix, and finish Mughniyah and anybody affiliated with him,” said a former U.S. official who served in Baghdad.

In January 2007, Bush, in an address to the nation, singled out Iran and Syria, two countries with the closest ties to Hezbollah.

“These two regimes are allowing terrorists and insurgents to use their territory to move in and out of Iraq,” Bush said. “Iran is providing material support for attacks on American troops. We will disrupt the attacks on our forces. We will interrupt the flow of support from Iran and Syria. And we will seek out and destroy the networks providing advanced weaponry and training to our enemies in Iraq.”

Shortly after Bush’s speech, Hezbollah’s involvement in Iraq became clearer. On Jan. 20, 2007, five American soldiers were killed in Karbala. That March, Ali Mussa Daqduq, a senior Hezbollah operative with ties to Mughniyah, was captured by the British along with two others and turned over to US forces.

While in US custody, Daqduq confessed to playing a key role in the killing of the soldiers and provided the United States with a deeper understanding of Hezbollah’s networks, said Peter Mansoor, a retired Army colonel who served as executive officer to Gen. David H. Petraeus, the top American commander in Iraq.

“In interrogations with these folks, we finally discovered the full nature of Iranian and Hezbollah involvement in Iraq,” Mansoor said, noting that by then Iran had “outsourced the advisory effort to Hezbollah.” Mansoor said he had no knowledge of the operation that killed Mughniyah.

US officials said Mughniyah played a pivotal role in linking Hezbollah to the Shiite militias that were working with Iran. It remains unclear if he ever entered Iraq. One former US senior military official said there was information he traveled to Basra in southern Iraq in 2006, but it was not confirmed.

Ryan C. Crocker, the US ambassador in Iraq when Mughniyah was killed, said: “All I can say is that as long as he drew breath, he was a threat, whether in Lebanon, Iraq, or anywhere else. He was a very intelligent, dedicated, effective operator on the black side.”

Crocker said that he didn’t know anything about the operation to kill the Hezbollah operative and had doubts about Mughniyah traveling to Iraq. That said, he added: “When I heard about it, I was one damn happy man.”

Terrorism discussion widens

US officials had explored ways to capture or kill Mughniyah for years. Those scenarios gained new urgency in the years after the Sept. 11 attacks when the Bush administration turned to the CIA and the US military’s elite Joint Special Operations Command for stepped-up plans to stop major terrorist operatives—including those without ties to al-Qaeda or the 9/11 plot.

A former US official described a secret meeting in Israel in 2002 involving senior JSOC officers and the chief of the Israeli military intelligence service. Amid a broader discussion of counterterrorism issues, the JSOC visitors raised the prospect of killing Mughniyah in such an offhanded fashion that their Israeli hosts were stunned.

“When we said we would be willing to explore opportunities to target him, they practically fell out of their chairs,” the former US official said. The former official said that JSOC had not developed any specific plan but was exploring scenarios against potential terrorism targets and wanted to gauge Israel’s willingness to serve as an evacuation point for US commando teams.

The former official said that the JSOC approach envisioned a commando-style raid with US Special Operations teams directly involved, not the sort of cloak-and-dagger operation that occurred years later.

“It never went anywhere,” said the former official, who was unaware of the CIA-Israeli operation to kill Mughniyah.

Still, the 2002 encounter suggests that Mughniyah continued to be a focus for US counterterrorism officials even after their overwhelming attention had shifted to al-Qaeda.

“We never took our eye off Hezbollah, but our plate was full with al-Qaeda,” said Bernazzani, who retired from the FBI in 2008 and said he had no knowledge of the operation to kill Mughniyah.

A window of opportunity

It is not clear when the CIA first realized Mughniyah was living in Damascus, but his whereabouts were known for at least a year before he was killed. One of the former US intelligence officials said that the Israelis were first to approach the CIA about a joint operation to kill him in Damascus.

The agency had a well-established clandestine infrastructure in Damascus that the Israelis could utilize. Officials said the Israelis wanted to pull the trigger as payback. “It was revenge,” another former official said. The Americans didn’t care as long as Mughniyah was dead, the official said, and there was little fear of blowback because Hezbollah would most probably blame the Israelis.

Amos Yadlin, the former head of Israeli military intelligence until 2010, said Mughniyah was positioned right under the group’s leader Hassan Nasrallah.

“He was the commander and chief of all military and terror operations,” Yadlin said, who declined to discuss Mughniyah’s demise. “He was the agent of the Iranians.”

The operation to target Mughniyah came at a time when the CIA and Mossad were working closely to thwart the nuclear ambitions of Syria and Iran. The CIA had helped the Mossad verify that the Syrians were building a nuclear reactor, leading to an Israeli airstrike on the facility in 2007. Israel and the United States were actively trying to sabotage the Iranian nuclear program.

Once Mughniyah was located in Damascus, the intelligence agencies began building a “pattern of life” profile, looking at his routine for vulnerabilities.

Mossad officials suggested occasional walks in the evening—when Mughniyah was unescorted—presented an opportunity. CIA officers with extensive undercover experience secured a safe house in a building near his apartment.

Planning for the operation was exhaustive. An Israeli proposal to place a bomb in the saddlebags of a bicycle or motorcycle was rejected because of concerns that the explosive charge might not project outward properly. The bomb had to be repeatedly tested and reconfigured to minimize the blast area. The location where Mughniyah was killed was close to a girls’ school.

One official said the bomb was tested many times at Harvey Point, a facility in North Carolina where the CIA would later construct a replica of Osama bin Laden’s compound in Abbottabad, Pakistan. Officials eventually concluded they had a bomb that could be used with no risk of others being killed or injured.

Mughniyah wasn’t alone in his confidence to operate freely in Damascus. During the operation, the CIA and Mossad had a chance to kill Qassem Soleimani, commander of Iran’s Quds Force, as he and Mughniyah walked together. Soleimani was an archenemy of Israel and had also orchestrated the training of Shiite militias in Iraq.

“At one point, the two men were standing there, same place, same street. All they had to do was push the button,” said one former official.

But the operatives didn’t have the legal authority to kill Soleimani, the officials said. There had been no presidential finding to do so.

When the bomb used to target Mughniyah was detonated, officials estimated the “kill zone” extended approximately 20 feet. The bomb was “very shaped and very charged,” an intelligence official recalled.

There was no collateral damage. “None. Not any,” the official said.

Facial recognition technology, another former official said, was used to confirm Mughniyah’s identity after he walked out of a restaurant in his neighborhood and moments before the bomb was detonated.

After the attack, Hezbollah leader Nasrallah blamed Israel for the killing and swore revenge: “Zionists, if you want an open war, let it be an open war anywhere.”

In fact, the damage to Hezbollah may have been compounded by the fact that the man charged with exacting revenge on Israel was a suspected Israeli asset. He was recently reported to be on trial in a Hezbollah court in Lebanon, but the group’s leader has downplayed the spy’s importance.

In a statement in 2008 after Mughniyah’s death, the office of then Israeli Prime Minister Ehud Olmert’s office said: “Israel rejects the attempt by terror groups to attribute to it any involvement in this incident. We have nothing further to add.”

State Department spokesman Sean McCormack said at the time: “The world is a better place without this man in it. He was a coldblooded killer, a mass murderer, and a terrorist responsible for countless innocent lives lost.”

Inside the intelligence community, a former official recalled, “It wasn’t jubilation.”

“We did what we had to,” the official said, “and let’s move on.”

William Booth in Jerusalem and Greg Miller, Karen DeYoung, Anne Gearan, and Julie Tate in Washington contributed to this report.

Adam Goldman reports on terrorism and national security for The Washington Post.

Ellen Nakashima is a national security reporter for The Washington Post. She focuses on issues relating to intelligence, technology, and civil liberties.

By Adam Goldman and Ellen Nakashima/www.washingtonpost.com