SIRTE, Libya — Sitting in a depression in the sand, behind a dune and surrounded by a handful of sorry-looking shrubs, was what the whole world is worried about.

There, under the baking sun on the outskirts of one of the most war-torn cities in Libya earlier this week, were crates full of the kind of surface-to-air missiles that could take down a jetliner.

They didn't appear to belong to anyone. There was no one guarding them and no one took notice when Peter Bouckaert, the emergencies directory for Human Rights Watch, began tearing into them.

He’d already trolled through scores of green wooden boxes scattered across Libya's sandy slopes, some of them full of bombs, rockets and shells — some of them long emptied.

But it was these kinds of surface-to-air missiles, known as SAMs, that foreign governments and aid organizations alike are terrified will end up in the wrong places and in the wrong hands.

It is widely believed that many of these weapons have already made their way out of the country. According to Israeli officials, Libyan munitions had been arriving in Gaza for months.

Related: Libya's missing weapons being smuggled into Gaza

The U.S. State Department, meanwhile, has made it a priority to try and track and dismantle the dangerous missiles, earmarking $40 million for the search.

But Bouckaert said it may have joined the hunt too late.

This week three State Department contractors, who declined to be named, met with Bouckaert in Misrata to gather information on the weapons sites around Sirte.

“It would have been nice if you guys had gotten here earlier,” Bouckaert told them.

“Well, yeah, that’s the government,” one of the contractor's said.

They asked Bouckaert if the Misrata brigade who had led him to the missiles answered to the Ministry of Defense.

“The MoD’s authority doesn’t extend beyond their hotel,” Bouckaert replied.

“The U.S. State Department has acted with a lot of sincerity,” Bouckaert told GlobalPost. “But they’ve always been a day late to secure these weapons — they were in Benghazi when the weapons were in Tripoli, and in Tripoli when they should be in Sirte. Now it’s going to cost them a lot more to track these weapons.”

And in Libya, these weapons are everywhere. About 20,000 surface-to-air missiles existed inside Libya before the revolution began, according to some estimates.

Libya: Mass proliferation of small arms worries authorities

Two days after Sirte’s fall and Muammar Gaddafi’s death, rebel forces from Misrata were pulling their stakes out of the ruins of what had been one of Libya’s richest cities. Sirte was a shattered ghost town with no water, electricity or residents.

The Sdada Martyr’s Brigade parked their hallmark all-black gun trucks in front of the metal containers they’d been sleeping in for more than a month to pack up. They hauled their mattresses, teapots, generators, and even a tank. And they filled one dump truck with a cache of former loyalist munitions, including seven SAMs.

The green, five-foot long SA-24 missiles were piled together in back like a set of discarded golf clubs.

“The scale of weapons in Libya is 10 times greater than in post-war Iraq,” Bouckaert said as he took pictures and catalogued the missiles' identification numbers in an effort to determine where they came from.

Such missiles can hit an airplane flying 10,000 feet in the air using a heat-seeking warhead. A shoulder-fired SA-7 hit an Airbus operated by DHL in Baghdad in 2003, forcing a controlled landing after the hydraulic system failed

Bouckaert said the plethora of unsecured surface-to-air missiles had been one of his biggest concerns since his team arrived at the start of the revolution in February.

“In Tripoli in August we found storehouses of landmines, anti-tank mines, also lots of looted surface-to-air missiles,” Bouckaert said. “What disappears first is surface-to-air missiles and hand-held weapons.”

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Although the ability of such missiles to shoot down an airliner is serious cause of alarm for the United States and other governments, Nicholas Marsh, a research fellow at the Peach Research Institute in Oslo, said he had doubts about the threat.

Surface-to-air missiles have been available for decades but a civilian airliner has rarely ever been targeted.

“The operation, maintenance and successful launch of a missile requires skills and equipment that aren't possessed by groups that might aim to bring down a civilian airliner,” he said.

He also doubted that the missiles were even still functional.

“I'm not convinced about the condition of the SA-7s found in Libya,” Marsh said. “My impression is that Gaddafi's regime just let huge quantities of material sit gathering dust in depots for decades.”

The missiles Bouckaert found, however, were still wrapped in plastic and had their batteries attached.

The more immediate threat might be from regional militant groups in the Middle East and Africa like Hamas and Hezbollah, which have more advanced training and state-funded budgets.

“[One] concern is that the missiles might get into the hands of a government,” Marsh said. “Those that are under embargo, and the rationale for them to obtain arms from Libya is clear. They couldn't legally buy such missiles on the international market, and so they will attempt to obtain them through illicit channels. The main concerns would be of Hezbollah, Sudan, Iran.”

Bouckaert agrees that surface-to-air missiles would be most dangerous in places like Gaza and Chad, but doesn’t want the world to forget that plain old tank shells, like the kind he found stacked to the ceiling at Hoshu Milhey, an unguarded complex of 70 warehouses 100 kilometers south of Sirte, have killed hundreds of soldiers in Iraq and Afghanistan because they can easily be made into improvised explosive devices, or IEDs.

“We could have pulled an 18-wheeler here and taken as many weapons as we wanted,” he said of the completely unguarded facility that the rebels had already looted for handheld weapons and anything they could mount on pickup trucks.

At the weapons depot in Sirte, Bouckaert said he had tracked 389 boxes of surface-to-air missiles using the shipment numbers marked on the crates and the packing lists inside. At the weapons site at Hoshu Milhey, he found upwards of 10,000 tonnes of bombs and missiles.

Munitions crates, he said, were scattered across the desert floor as far as the eye could see.