By Thom Patterson

CNN

(CNN) -- For years, US authorities were desperate to get their hands on a man they called the "Peacock," a Syrian-born weapons dealer said to be behind some of the world's most notorious acts of violence.

The man, whose real name is Monzer al-Kassar, got rich by selling weapons and military equipment to terrorists and armies fighting in Iraq, Iran, Africa, Eastern Europe, Central America and elsewhere, according to the US Drug Enforcement Agency.

By doing so, Kassar fueled several of the deadliest wars and terror attacks of the past 35 years, including the 1985 hijacking of a cruise ship that left a retired Jewish-American businessman dead. The DEA says Kassar armed the Palestinian terrorists behind the attack.

All along, Kassar flaunted his money with an expensive lifestyle, including fancy clothes, cars and lavish estates, which is what gave him the nickname "the Proud Peacock."

DEA agents described him as a "global criminal" who eventually grew to become one of the top five weapons dealers in the world. "But to try to lock up an international arms trafficker, you're dancing with the devil," said Nicholas J. Nargi, DEA assistant special agent in charge.

Kassar remained elusive until 2007, when an intricately choreographed DEA sting operation finally brought him down. Only now are new details emerging about that dramatic arrest, as part of CNN's Original Series "Declassified."

But Kassar proved to be a very cautious man, and that nearly derailed the entire operation.

Achille Lauro

The 1985 terror attack by the Palestinian Liberation Front on the Italian cruise ship Achille Lauro shocked the world.

"Monzer was the supplier of the weapons," said James Soiles, retired DEA chief of global operations. "He brought the weapons from Poland and turned them over to the fighters."

During the attack, terrorists shot and killed passenger Leon Klinghoffer --- who used a wheelchair --- and threw him overboard.

In addition to providing the weapons, Nargi said, Kassar also "provided the logistics for the hijacking of the ship."

The setup

For decades, trying to capture an elusive international criminal like Kassar, who had ties to many nations, was difficult under US law. But after the 9/11 attacks in 2001, laws were changed to allow the arrest of suspects outside the United States for prosecution in federal courts.

Those new laws gave the DEA a green light to begin building a case against Kassar in hopes of bringing him down.

By 2006, agents found a source who could connect them with Kassar. The DEA devised a plan to capture him and began assembling a team.

Two confidential DEA sources met with Kassar in Beirut, where a deal was initially proposed. Next, two other confidential DEA sources from Central America -- going by the names Carlos and Luis -- agreed to pose as weapons buyers from the South American rebel group, FARC. The organization, whose name is a Spanish acronym for the Marxist Revolutionary Armed Forces of Colombia, was considered a terrorist group by the United States.

Carlos and Luis agreed to meet Kassar at his lavish estate in Marbella, Spain.

The wire

During the dangerous undercover meeting at Kassar's mansion in 2007, Carlos and Luis were wired with audio and video recording equipment.

"This kind of operation goes against everything you've ever been taught as a cop going undercover," said Nargi. "You always want to meet in a neutral place. You always want to be in control of the situation. And here we are -- we're going to have no control over the situation at all. We're just hoping that everybody can get out of there safely and come home."

As Soiles put it: "If the meeting didn't go in the right direction, we were going to lose him."

A cautious Kassar tried to test Luis and Carlos' knowledge of FARC, but once he was satisfied, he agreed to sell them more than 12,000 weapons, including surface-to-air missiles that would be used by FARC to shoot down American helicopters.

The deal also included an offer by Kassar to send 1,000 fighters to bolster FARC forces, plus explosives and trainers to show FARC how to use them.

Kassar demanded $4.4 million as "partial payment" for the weapons.

"We had great evidence because of how he talked about how his business with us could lead to American deaths," Nagi told CNN's "Declassified."

The take down

Once the deal was set, the DEA wanted to arrange a meeting with Kassar in a place where he could be most easily extradited to the United States.

As bait, Luis and Carlos told Kassar that a high-ranking FARC member would be traveling specifically to pay Kassar. He was told the FARC leader would hand over the money to Kassar if he personally saw him, to confirm that Kassar was involved in the deal.

When Luis and Carlos proposed they meet in Romania, where he could more easily be extradited to the United States, Kassar balked. The idea of leaving Spain made him nervous.

Instead, the meeting was arranged for Madrid International Airport. When Kassar flew from his estate to the airport, Spanish police --- accompanied by DEA agents --- were there, ready to nab him.

But immediately after Kassar deplaned and entered the airport terminal, DEA agents suddenly lost track of him, spurring a moment of panic.

A few minutes later, agents breathed a sigh of relief when he was spotted coming out of an airport public restroom.

Shortly after that, police descended on Kassar, slapping him in cuffs and putting him aboard a jet to the United States.

In US federal court, Kassar pleaded not guilty to all charges, including conspiring to kill United States citizens and supporting a "designated foreign terrorist organization."

After a trial, jurors found him guilty and Kassar was sentenced to 30 years in prison.

Now 72, Kassar is serving his sentence at a federal prison in Marion, Illinois, about 300 miles from Chicago. He's not scheduled to be released until 2033, when he'll be 88 years old.