Since the September 11th, 2001 terrorist attacks in the United States, protecting the nation's borders has been a critical component of guarding against future terrorist threats. One of the most vital regions is on the 6500-kilometer long U.S. Canadian border. Security officials at one of the busiest northern crossings need to strike a balance between guarding America's border and maintaining the free flow of trade.

It is one of the busiest ports of entry along the U.S. Canadian border. Each year tens of thousands of vehicles along with millions of people come through the Blaine border checkpoint that separates the western U.S. state of Washington and British Columbia, Canada.

The border crossing is also one of the most active smuggling corridors on the northern border.  U.S. Customs Chief Inspector Phillip Stanford has seen criminals try to smuggle drugs, weapons and money through here. Customs officers searched a pickup truck after noticing something wasn't right.

"Another agent is going around the truck just tapping, trying to make sure things sound right and if they do not sound right,? said Inspector Stanford. ?Well, they heard this and that is not right. They (the agents) finally got two fork lifts and popped the compartment and inside was two large packages that contained multiple bags of U.S. currency, $114,000 in cash."

Mr. Stanford and other enforcement officers are also on the lookout for international terrorists. They know any one of these cars, buses, or trucks might be carrying terrorists and concealing weapons of mass destruction.

On this day, officers swarm around a car for an arrest after the driver's name initially appears on the U.S. terrorist watch list. This time, it turned out to be a false alarm. But it illustrated the heightened security in place to prevent known terrorists from getting into the country.

Inspector Stanford, explains, "We are looking to see if people have traveled to countries where al-Qaida has their training camps.  We know they have had training camps down in Oregon and they have a couple of cells up in Vancouver, Canada which is just 30 miles [48 kilometers] north of us."

Since 1995 federal authorities have caught more than a dozen known terrorists trying to enter the country from Canada. Two of the arrests were made at the Blaine crossing.

Security expert James Carafano is with the Heritage Foundation in Washington, D.C.  "Virtually every known terrorist that has ever tried to enter the United States that we know of has tried to come in through a legal means, with a visa that they either legitimately have or have fraudulently or through a legal point of entry. So that is the first point in border security is to start at the places where people legally and goods and services cross the border," he said.

Security at the Blaine crossing has greatly improved since September 11th, 2001. Customs inspectors now use radiation scanners and gamma-ray imaging systems that can look inside cars and truck trailers without having to open them.

Jay Brandt, Assistant Port Director, says the machines can scan the cargo for items emitting radiation including a radioactive or dirty bomb. " We certainly hope this technology will identify the threat."

U.S. Customs officials say improving inspections at ports of entry will not only facilitate the free flow of legitimate goods and traffic but also better secure the nation's borders to prevent terrorists and their weapons from entering the United States.