Alarmed, the officer, Capt. Joseph Naddaf of the State Security agency, warned his superiors about what appeared to be an urgent security threat.

But it turned out that other Lebanese officials already knew. Lots of officials.

An investigation by a team of New York Times reporters who conducted dozens of interviews with port, customs and security officials, shipping agents and other maritime trade professionals revealed how a corrupt and dysfunctional system failed to respond to the threat while enriching the country’s political leaders through bribery and smuggling.

Previously undisclosed documents lay out how numerous government agencies passed off responsibility for defusing the situation. Exclusive photographs from inside the hangar show the haphazard, and ultimately catastrophic, handling of explosive materials. And an analysis of high-definition video illustrates how the volatile cocktail of combustible substances came together to produce the most devastating explosion in Lebanon’s history.

In the six years since the 2,750 tons of ammonium nitrate had arrived in Beirut’s port and been offloaded into Hangar 12, repeated warnings had ricocheted throughout the Lebanese government, between the port and customs authorities, three ministries, the commander of the Lebanese Army, at least two powerful judges and, weeks before the blast, the prime minister and president.

No one took action to secure the chemicals, more than 1,000 times the amount used to bomb a federal building in Oklahoma City in 1995.

The disaster-in-waiting was the result of years of neglect and bureaucratic buck-passing by a dysfunctional government that subjugated public safety to the more pressing business of bribery and graft.

Perhaps nowhere is that system more pronounced than at the port, a lucrative prize carved into overlapping fiefs by Lebanon’s political parties, who see it as little more than a source of self-enrichment, contracts and jobs to dole out to loyalists, and as a clearinghouse for illicit goods.

In seconds, the explosion had punched through buildings for miles around, collapsing historic homes, reducing skyscrapers to hollow frames and scattering streets with the detritus of countless upended lives. The blast killed more than 190 people, injured 6,000 and caused billions of dollars in damage.

Government dysfunction had already brought Lebanon to the brink of ruin, with an economy on the verge of collapse, shoddy infrastructure and a persistent antigovernment protest movement. The explosion overshadowed all that, raising alarm about the system’s inadequacy in a vivid and frightening new way.

The port is emblematic of everything the Lebanese protesters say is wrong with their government, with dysfunction and corruption hard-wired into nearly every aspect of the operation.

The daily business of moving cargo in and out of the port, The Times found, requires a chain of kickbacks to multiple parties: to the customs inspector for allowing importers to skirt taxes, to the military and other security officers for not inspecting cargo, and to Ministry of Social Affairs officials for allowing transparently fraudulent claims — like that of a 3-month old child who was granted a disability exemption from tax on a luxury car.

Corruption is reinforced by dysfunction. The port’s main cargo scanner, for instance, has not worked properly for years, abetting the bribe-ridden system of manual cargo inspections.

Hours after the blast, the president, prime minister and the leaders of Lebanon’s security agencies — all of whom had been warned about the ammonium nitrate — met at the presidential palace to assess what had gone wrong. The meeting quickly devolved into shouting and finger-pointing, according to one attendee and others briefed on the discussion.

There was plenty of blame to go around. All of Lebanon’s main parties and security agencies have a stake in the port. None took action to protect it.

“There has been a failure of management from the birth of Lebanon until today,” Judge Ghassan Oueidat, Lebanon’s chief public prosecutor, said in an interview. “We failed at running a country, running a homeland.”

And running a port.

An Unscheduled Port of Call

In November 2013, a leaking and indebted Moldovan-flagged ship sailed into the Beirut port carrying 2,750 tons of ammonium nitrate. The vessel, the Rhosus, had been leased by a Russian businessman living in Cyprus and was destined for Mozambique, where a commercial explosives factory had ordered the chemical but never paid for it.

Beirut was not on the itinerary but the ship’s captain was told to stop there to pick up additional cargo, heavy machinery bound for Jordan. But after two companies filed suit claiming they had not been paid for services they provided to the ship, Lebanese courts barred it from leaving.

The Russian businessman and the ship’s owner simply walked away, leaving the ship and its cargo in the custody of Lebanese authorities. It remains unclear who owned the ammonium nitrate and whether it was intended to end up in Beirut or Mozambique.

A few months later, in the first of many documented warnings to the government, a port security officer alerted the customs authority that the ship’s chemicals were “extremely dangerous” and posed “a threat to public safety.”

Soon after, a Beirut law firm seeking the repatriation of the Rhosus’s crew to Russia and Ukraine urged the port’s general manager to remove the cargo to avoid “a maritime catastrophe.” The law firm attached emails from the ship’s charterer warning about its “EXTREMELY DANGEROUS CARGO” and a 15-page Wikipedia entry cataloguing “ammonium nitrate disasters.”

Fearing the dilapidated ship would sink in the harbor, a judge ordered the port to offload the cargo. In October 2014, it was transferred to Hangar 12, a warehouse designated for hazardous materials.

Bags of ammonium nitrate were piled haphazardly near the fuel and fuses and on top of some of the fireworks.

“You’re putting all the ingredients into a box, and you’re playing a dangerous game,” Dr. Glumac said. “This is an accident waiting to happen.”

Ali Baba’s Cave

The Lebanese sarcastically refer to a place known for corruption as “Ali Baba’s cave,” the hiding place for stolen treasure in the Arab folk tale. The Beirut port, on the Mediterranean coast near downtown Beirut, has long been seen as the cave with the most treasure.

After the Aug. 4 explosion, government prosecutors launched an investigation and have since detained at least 25 people connected to the port. But the investigation is unlikely to change the culture of gross mismanagement that set the stage for the explosion, and which is built into the port’s operations.

The port is the gateway for three-quarters of Lebanon’s imports and nearly half its exports. That trade, estimated at $15 billion a year before the economy began sinking last year, provides bountiful opportunities for corruption and the political parties have built rackets to each get their cut.

The port’s operation mirrors Lebanon’s sectarian system of government in which top government posts are assigned according to sect, the main political factions compete for control of government agencies and party leaders carve up the country’s economic pie.

The system was aimed at ending sectarian warfare but left the country with a fractious, divided government. The peace agreement that ended Lebanon’s civil war in 1990 codified the system and turned militia commanders into party bosses, who set about stocking the state bureaucracy with their supporters.

“When the war ceased, they thought it would take a few years to integrate the militiamen into the state,” said Alain Bifani, who resigned this year after two decades as director of the Finance Ministry. “Instead, the heads of militias began running ministries and it was the civil servants who had to integrate. Slowly but surely, they became militiamen and we created small empires that ran the government.”

After the war, the government designated a “temporary committee” of six people linked to the main political parties to run it until a permanent arrangement could be found. That never happened, and the “temporary” committee still runs the port, with little government oversight. Its members have not changed in nearly two decades.

The parties installed their loyalists in key port jobs, where graft supplemented their salaries as security officers, administrators and customs inspectors and positioned them to spirit goods through the port for their patrons.

“The parties’ thinking is: ‘I put you there, you make a lot of money, and when I need you, you help me out,’” said Paul Abi Nasr, a board member of the Association of Lebanese Industrialists.

Gateway for Contraband

According to port employees, customs officials and shipping and customs agents, little moves in the port without bribes being paid, goods fly through with little or no vetting, and evasion of the law is the rule, not the exception.

In addition to depriving the government of sorely needed revenue, corruption has made the port a gateway for contraband in the Middle East, allowing arms and drugs to slip through virtually unimpeded.

The port security and military intelligence officials charged with enforcing regulations and keeping the port safe also exploit their authority for profit, port employees and shipping agents said, accepting what they euphemistically call “gifts” to let shipping containers avoid inspection.

So do customs officers, port and customs officials said. The port handles 1.2 million cargo containers a year, but its main cargo scanner has been out of order or offline for years, they said. That means that customs officers inspect containers manually, if at all, and routinely take kickbacks to sign off on unregistered, undervalued or miscategorized goods.

“Some traders buy certain items and show false receipts,” said Raed Khoury, a former economy minister. “If it costs $1 million, they will provide an invoice of $500,000 to pay less tax.”

One customs clearing agent said his small company spends $200,000 a year on bribes to move goods through the port.

The politically connected exploit exemptions for the disabled to import goods tax free, according to a customs official who has witnessed the transactions. Politicians turn up with notes from doctors attesting to a relative’s limp or hearing loss to avoid paying as much as $150,000 in duties on a Mercedes or Ferrari.

Last year, the official said, the Ministry of Social Affairs granted a 3-month-old infant with Down syndrome an exemption to import a luxury car tax free.

All the parties have agents at the port, although some have more clout than others.

The two main Shiite parties, the Amal Movement and Hezbollah, work together and have the most control, according to shipping companies and businessmen who use the port.

The Future Movement, a Sunni-led party headed by former Prime Minister Saad Hariri, and President Michel Aoun’s Free Patriotic Movement also have significant stakes.

The Druse-led Progressive Socialist Party, the Christian Lebanese Forces party and other smaller parties also have people inside to smooth the way when they need to move goods in or out.

The big parties have long taken advantage of tax exemptions for religious institutions, officials said. Tens of thousands of containers for the Supreme Islamic Shiite Council and Dar el Fatwa — a government body of Sunni clerics — enter customs-free each year, packed with T-shirts, electronics, floor tiles and even cars, which officials say are sold for profit. Christian and Druse political parties and institutions also exploit these exemptions, but on a smaller scale, officials said.

Officials at the Shiite Council and Dar el Fatwa denied that their organization imported anything other than supplies for mosques and donations for the needy.

Hezbollah, which the United States and other countries consider a terrorist organization, has a unique ability to move goods with no checks thanks to a well organized network of loyalists and allies in the port, according to port, customs and American officials.

United States officials say Hezbollah probably does not rely on the port to smuggle weapons, instead preferring the Beirut airport, which it controls, and Lebanon’s long and porous border with Syria. But merchants associated with the party smuggle goods through the port, American and port officials say, supplying tax-free items to Lebanon’s Shiite communities.

Hezbollah’s leader, Hassan Nasrallah, denied last month that his organization had any presence in the port.

Corruption costs the government dearly, with officials and diplomats estimating that unpaid customs duties, at the port and other points of entry, could add up to as much as $1.5 billion per year.

No one complains as long as the money keeps flowing.

“Everyone benefits,” a port auditor said, speaking on condition of anonymity, like others interviewed, for fear of retribution. “They go home happy, their pockets full.”

When a new customs director, Badri Daher, was appointed in 2017, he appealed to the Finance Ministry for money to buy a new cargo scanner and enough vehicles to patrol the port, and to update the department’s obsolete computer system, two customs officials said. The request was blocked by the Finance Ministry, they said.

But Lebanon’s finance minister at the time, Ali Hassan Khalil, said his ministry supported the request.

“The blocking came from other ministries, not ours,” he said in a telephone interview.

In any case, the broken scanner was never replaced.

Failure to Act

Judge Oueidat, the public prosecutor, said the military and the customs authority had the legal authority to remove the ammonium nitrate.

But when it was brought to their attention, neither did.

The port authority asked the Lebanese Army to take the chemicals in 2016, but the army chief, Gen. Jean Kahwaji, said in a written response that the military was “not in need of” ammonium nitrate. He suggested that the port offer it to a commercial explosives manufacturer or “return it to its country of origin.”

At least six times in three years, top customs officials sent letters to the judiciary about the cargo, noting “the serious danger posed by keeping this shipment in the warehouses” and asking the court to remove it “to preserve the safety of the port and its workers.”

But the letters were sent to the wrong office, according to lawyers and judicial officials, and the judges never issued new orders.

In 2018, the Rhosus sank in the harbor, where it remains. The cargo remained in Hangar 12.

It sat there last year, when hundreds of women and children ran by Hangar 12 during a race sponsored by the Beirut Marathon.

It was still there last September, when the American guided-missile destroyer Ramage docked at the port for exercises with the Lebanese Navy and the United States ambassador to Lebanon hosted a reception on board, a half-mile from Hangar 12.

A Hole in the Wall

There was no shortage of security agencies in the port that could have sounded the alarm about what amounted to a deconstructed bomb in Hangar 12.

The army’s intelligence branch and the General Security Directorate have large presences there, and the customs authority also has a security force.

In 2019, the State Security agency also opened a port office, led by Capt. Naddaf, who is now a major. During a patrol last December, he noticed the broken door and hole in the wall of Hangar 12 and his agency investigated.

The immediate worry was not an explosion, but that the chemicals would be stolen by terrorists.

State Security reported the issue to the state prosecutor’s office, and in May Judge Oueidat ordered the port to fix the hangar and appoint a supervisor. But no immediate action was taken.

Capt. Naddaf, who raised the alarm about the ammonium nitrate, was one of those detained by state prosecutors.

As to a later suggestion that a significant portion of the ammonium nitrate had been stolen or removed from the warehouse, independent calculations by Dr. Glumac and Dr. Oxley, based on the speed and destructiveness of the shock wave, estimated that it had not, and that most or all of it remained in the warehouse and had detonated.

A senior security official said that Prime Minister Hassan Diab was informed about the chemicals in early June and planned a visit to the port to raise the issue but cancelled it. A statement from Mr. Diab’s office described the visit as a “routine inspection” that had been postponed because of other, pressing matters.

In late July, State Security warned the country’s most powerful officials in a report to the High Security Council, which includes the heads of Lebanon’s security agencies, the president and the prime minister.

On Aug. 4, the government finally acted, sending a team of welders to fix the hangar.

It remains unclear whether their work accidentally lit the fire that caused the explosion that same day but that is the most likely scenario.

“If there was welding going on in the vicinity, that’ll do it,” said Van Romero, a physics professor and explosives expert at New Mexico Tech. “You have all the ingredients.”