Six former employees, including two former executives, of Germany's most notorious gunmaker, Heckler & Koch, will go on trial in Stuttgart on Tuesday over the illegal sale of thousands of G36 assault rifles to Mexico between 2006 and 2009 — a deal that violated both Germany's War Weapons Control Act and the Foreign Trade Act.

The deal's bloody consequences were demonstrated most obviously on September 26, 2014, when a bus full of Mexican teaching students was attacked in Iguala, Guerrero, by police. Six were shot dead, 40 were injured, and another 43 simply "disappeared," as thousands of others have in Mexico's ongoing drug war. It is believed that corrupt police officers turned the demonstrators over to a local mafia, the Guerreros Unidos, who murdered them and burnt the bodies.

By 2015, German and Mexican journalists and activists had proved beyond doubt that H&K guns were used during the attack. That revelation came out of a documentary aired by German public broadcaster ARD, which proved that the guns were being used in parts of Mexico that German law had forbidden, that Mexican government officials had no intention to sticking to this proviso, or were not even aware of it, and that H&K helped train police officers in the forbidden regions.

But it has still taken two more years — eight years after charges were initially filed by the anti-arms trade activist Jürgen Grässlin — for Stuttgart prosecutors to bring the case against the H&K employees to trial.

Read more: Mexico's missing students: more questions than answers

G3 — the global hit

But, as people like Grässlin and his RüstungInformationsBüro (Arms Information Office), are always at pains to point out, the fact that H&K got caught making an illegal deal is really no more than an opportunity to draw attention to a company that has, quite legally, flooded the world with small arms since its foundation in the small, secluded Black Forest town of Oberndorf in affluent Baden-Württemberg in 1949.

Local legend says that Edmund Heckler, an engineer at Mauser — which supplied thousands of rifles to Hitler's armies from a factory in Oberndorf — founded the company after hiding Mauser machinery from Allied forces tasked with demilitarizing Germany.

Of all the guns that H&K have made over the years, one rifle provides the best example of the company's impact on world conflicts: The G3 rifle, first manufactured in 1959 as the Bundeswehr soldier's standard weapon, is one of the most ubiquitous assault rifles in the world — some say second only to the Kalashnikov AK47.

Hundreds of thousands, if not millions, of people have been killed by G3s in the world's conflicts since their initial production. Because a well-maintained rifle can function for decades, the G3 has inevitably made its way into the hands of virtually every terrorist organization or extremist militia on every continent.

In the much less restrictive early days of German arms sales, successive West German governments approved the sale of G3s to 80 countries. But that wasn't how the gun truly became popular around the world: Between 1961 and 1981, Bonn also allowed H&K to sell licenses to manufacture G3s to 15 countries. This meant that Germany was effectively exporting machine-gun franchises directly to places that would, sooner or later, become conflict zones.

The countries that received G3 licenses over those two decades included Iran, Mexico, Myanmar (then known as Burma), Pakistan, the Philippines, Turkey and Saudi Arabia — all countries either involved in major wars, internal armed conflicts or proxy wars through militias like Hezbollah. For this reason, it is virtually impossible to ascertain exactly how many G3s are still in circulation, though it is likely to be at least 7 to 10 million.

Read more: German weapons firms find lucrative market in US

G36 — the even deadlier sequel

That story was repeated with the weapon that became the G3's successor in the German military, and the gun at the center of Tuesday's trial in Stuttgart — the G36: first manufactured in 1997 and capable of even greater power and accuracy than the G3.

By the time the G36 began to be sold around the world, German export controls had become much stricter, and licenses were only granted to Spain and Saudi Arabia. Mexico was also in talks to get a license, but those broke down when Mexico introduced its own FX-05 Xiuhcoatl weapon in 2006, which many noted was suspiciously similar to the G36, and which is the subject of another investigation into whether H&K secretly sold expertise to help Mexico.

Still, in its relatively brief 20-year history — and despite Germany's stricter controls — the G36 has found its way into the hands of state and non-state belligerents around the world, including Egypt, Moammar Gadhafi's Libyan army, Kurdish peshmerga fighters in northern Iraq, and the Saudi Arabian army and police force.

But the many years of protests, the upcoming trial, and the media attention that the illegal Mexico G36 deal has dragged with it, has had a noticeable impact on Heckler & Koch: On May 11, just days before the trial was due to begin, the company released a fairly momentous statement confirming a policy change first reported last year:

"Our products will from now on only be delivered to states that as 'green countries' fulfill clear and justifiable criteria," it read. "This includes states that belong to EU or NATO or have concluded association agreements with NATO, and additionally fulfill further conditions." That would imply that on paper H&K's own ethical standards appear to be effectively stricter than those of the German government.