Today's viral home video by a witness to the attack on the Charlie Hebdo offices in Paris shows two shooters walking calmly towards their get-away car, before slowly driving away. Both were carrying large Kalashnikov-style assault rifles.

Now, in the aftermath of the attack that President Francois Hollande calls an act of terrorism – many are wondering how the suspects procured weapons considered here as useful mainly in a war.

Unlike relatively lax US gun regulation, French laws are highly restrictive, especially for assault weapons. After the Hebdo attack, gun control laws will likely get prominent attention here.

But tightening legal arms sales is likely to be less important and certainly less challenging than cracking down on the sizable illegal arms trade in France and across Europe.

For every legal firearm in France, for example, there are nearly two illegal ones, experts say. While the exact number is not known, estimates run to 10 to 20 million illegal weapons in circulation in France’s population of 65 million.

If the Hebdo attackers did carry legally-acquired weapons, they would first had to negotiate strict laws. Applying for a gun license for hunting, target shooting, or personal protection requires not only a background check but a formal psychological evaluation. Gun licenses must be renewed every three to five years; the blacklist of those banned from owning weapons is nearly 18,000.

And laws regulating automatic or semi-automatic weapon ownership is even more restrictive. Following the 2012 shooting spree in Toulouse by Islamist gunman Mohammed Merah, punishment for possessing such weapons is harsher.

However, it is unlikely the suspects in the Charlie Hebdo attack had valid firearm licenses or bought their weapons legally, experts say. Rather, they were likely procured from a black market of weapons that in France and Europe is wide and deep. The hub of one of the largest Internet trafficking rings is thought to be in Paris.

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In October of this year, 48 people were arrested after raids in France found hundreds of illegal arms stashed away. The seized caches included machine guns, assault rifles, and automatic pistols.

But it would be overly optimistic to assume that the October raid wiped out France’s illegal arms trade. Finding and buying a weapon online requires simply logging on to one of several websites, and adopting a pseudonym. A click of the mouse enables one to buy a black-market Kalashnikov for between $2,000 and $4,000 dollars. A handgun goes for just over $1,000 dollars.