(CNN) -- At the Eslam Ghalah crossing on the Afghan-Iranian border, millions of dollars have been spent by the international community to try to ensure that all goods and human traffic entering and leaving Afghanistan can be controlled and accounted for.
But we found a very different reality.
We had traveled from the city of Herat in out to Afghanistan's western border to film a story on the smuggling of weaponry to the Taliban from Iran - we wanted to get a sense of how much was being done to block the smuggling trails along the Iranian border -- an area of remote mountain trails and passes.
The local security commissioner had insisted we take a police escort. Once we had finished filming at the official crossing I asked the commander of the detail if he knew where the main smuggling trail across the border was as I'd heard it was just outside of Eslam Ghalagh.
He agreed to take us and we climbed back into our cars.
Less then five minutes later we turned off the main road onto a dusty track. Another five minutes and the police car leading the way came to a halt - we were less than 10 kilometers from the official crossing and we'd arrived.
It was the best known smuggling trail, but just one of many hundreds of trails that snake through the mountains here.
Afghanistan's border with Iran is around 1,000 kilometers long. There is no doubt that it's one of the most difficult in the world to police.
But all the Afghans we spoke to were adamant that while the Iranians are deadly serious about blocking the drug trade into Iran from Afghanistan, they are much less rigorous about the traffic in weapons in the other direction.
And the sources we spoke with - Afghan, Taliban and Western - believe that is a matter of policy.
But it's far from clear at what level in the Iranian government -- if any -- the arms shipments are organized or approved.
For their part, the Iranians strenuously deny involvement in the smuggling. The Embassy in London told me: "These allegations are fabricated to pervert attentions from the problems and damage created by foreign forces in [Afghanistan."]
Getting people to talk about the smuggling on camera was almost impossible.
It's no overstatement to say that many Afghans in Herat are scared of their powerful neighbor to the West.
Nearly everyone who gave us information did so on condition of anonymity.
Several of the officials we interviewed happily gave us access to their records and reports but as soon as the camera was switched on the stock response was that they were not authorized to comment.
On our last day in Herat we finally were given access to the evidence store where the weaponry seized along the border was kept.
The source helping us had to resort to locking us in his office after smuggling an Iranian mine out of the store room so we could film it. It was same kind as those used by the Taliban in roadside bomb attacks.
Later that day, a very senior contact in the Afghan security services gave us access to the Afghan police's evidence file.
Although the International Security Assistance Force in Afghanistan has made numerous statements about Iranian weaponry and training being provided to the Taliban the Afghan government has remained largely silent.
In Herat the provincial authorities have spent the last two years filming every weapon haul they've intercepted coming over the Iranian border, photographing serial numbers written in Persian and establishing which models are produced in Iranian state armament factories.
If the Afghan government decides to take up the issue with Tehran, they'll find all the evidence they need here in Herat.
