A team of UN chemical weapons inspectors, who have been in Damascus for several days gathering evidence of a possible chemical weapons attack near Damascus on August 21, left Syria early Saturday morning, crossing into Lebanon. This came just hours after US President Barack Obama said he was weighing “limited and narrow” action against a Syrian regime that the administration has bluntly accused of launching the deadly attack which it says killed 1,429 people.

The team left its Damascus hotel early Saturday and made its way to the neighboring state from which it will head on to the Netherlands.

Meanwhile, a 6th US warship, the USS San Antonio, has joined the five Navy destroyers currently in the Mediterranean Sea waiting for the order to launch. The USS San Antonio is an amphibious assault ship, which is carrying helicopters and some 300 Marines, according to reports, but it has no cruise missiles, so it is not expected to participate in the attack. Instead, the ship’s long-planned transit across the Mediterranean was interrupted so that it could remain in the area to help if needed.

The destroyers are armed with dozens of Tomahawk cruise missiles, which have a range of about 1,000 nautical miles and are used for deep, precise targeting. Each one is about 20 feet long and less than two feet in diameter and carries a 1,000 pound warhead. The missiles fly at low altitudes, and their range allows the ships to sit far off the coast, out of range of any potential response by the Syrian government.

The inspectors’ departure brings the looming confrontation between the US and President Bashar Assad’s regime one step closer to coming to a head.

The USS San Antonio, an amphibious assault ship, carries helicopters and Marines but no cruise missiles. (Photo credit: US Navy photo by Mass Communication Specialist 3rd Class John K. Hamilton/Released/Wikipedia)

The USS San Antonio, an amphibious assault ship, carries helicopters and Marines but no cruise missiles. (Photo credit: US Navy photo by Mass Communication Specialist 3rd Class John K. Hamilton/Released/Wikipedia)

And as the international community dithers on how to respond to the reported use of chemical weapons by the regime, the UN inspectors will arrive in the Netherlands — having endured repeated delays, unrelenting scrutiny and even snipers’ bullets in Damascus over the course of their stay — to set in motion a meticulous process of analyzing samples at specially accredited laboratories.

According to the team’s UN mandate, the analysis will establish if a chemical attack took place, but not who was responsible for a deadly August 21 attack that Doctors Without Borders says killed 355 people and included the use of toxic gas. US Secretary of State John Kerry said Friday that Washington knows, based on intelligence, that 1,429 people were killed, and that the Syrian regime carefully prepared for days to launch the chemical weapons assault.

UN Secretary-General Ban Ki-moon is expected to get an initial briefing on the UN team’s work this weekend from disarmament chief Angela Kane, but it remains unclear exactly how long the process of examining samples will take.

UN spokesman Martin Nesirky said the team had concluded its collection of evidence, including visits to field hospitals, interviews with witnesses and doctors, and gathering biological samples and environmental samples.

The Organization for the Prohibition of Chemical Weapons, which provided most of the 12-strong team of inspectors, has stringent guidelines for handling and testing samples at a chain of special labs around the world to ensure it delivers unimpeachable results — which could have far-reaching ramifications once they are reported at the United Nations in New York.

“It has to be accurate. The procedure has to be absolutely rigid and well-documented,” former OPCW worker Ralf Trapp told The Associated Press on Friday.

Key to the procedure is a rock-solid chain of custody rules for the samples and analysis of each sample by two or possibly three different labs. The OPCW works with 21 laboratories around the world that have to pass a proficiency test each year to ensure their work meets the organization’s standards.

Strictly documenting who has had custody of samples every step of their journey from the chaos of a Damascus war zone to the sterile serenity of a specially certified lab ensures that the material to be tested is what the inspectors say it is.

The labs, and even the inspectors themselves, will likely have been chosen from countries with a neutral stance on the Syrian conflict, experts say. Inspectors at the OPCW generally are analytical chemists and chemical weapons munitions experts.

Samples they gather are put in vials that are sealed and then put in a transport container that is also secured with a fiber-optic seal, said Trapp, who is now an independent disarmament consultant. Every time the container changes hands it is documented.

“A lot of stuff is built into the system to make sure nobody has tampered with the samples or replaced one with another,” he said.

Once they have taken custody of the samples, chemists at the laboratories will test them for traces of chemicals banned under the Chemical Weapons Convention. The samples will be sent to two or three labs whose results will be cross-checked to ensure they match up, again reducing the chance of an inaccurate result.

The inspectors’ mission has been shrouded in as much secrecy as is possible in Syria and will remain so once the team returns to the Netherlands.

There has been no official word on what type of samples they have gathered, but media reports suggest they collected soil that could be contaminated and swipes from munitions, along with blood and hair samples from victims and possibly even tissue from corpses, Trapp said.

Officials at the OPCW, headquartered in The Hague close to the UN’s Yugoslav war crimes tribunal and the European Union’s Europol police organization, say team members will make no comment on their return.

That means the first time their full findings are expected to be known will be after they are sent to UN headquarters in New York.

What remains unclear is when exactly that will happen. Trapp said the painstaking testing will take several days and the labs working on the samples won’t sacrifice accuracy for the sake of quick results.

“In the current situation they would probably be pressed to speed up as much as they can, but there’s always the risk if you speed it up too much that you will end up with results that could be contested by somebody,” he said.