The man arrested in Phuket, Joseph Hunter, went by the nickname "Rambo" and had trained snipers for the Iraq and Afghanistan wars before leaving the army and turning rogue, prosecutors allege.
A law enforcement sting in Bangkok and Liberia interrupted their plans to use five ex-military snipers to protect illegal drug shipments, authorities said.
The charges were announced by prosecutors in Manhattan, where an indictment unsealed in federal court portrayed a trio of ex-soldiers eager to kill for money.
"That's fun, actually for me that's fun. I love this work," one was quoted as saying in court papers.
The documents described numerous conversations at meetings outside the United States that were recorded by Drug Enforcement Administration (DEA) agents building their case with help from confidential sources posing as drug traffickers.
The defendants were charged with conspiracy counts and were held for appearances in US District Court, though it was not immediately clear who would represent them.
"The bone-chilling allegations in today's indictment read like they were ripped from the pages of a Tom Clancy novel," US Attorney Preet Bharara said in a statement. "The charges tell a tale of an international band of mercenary marksmen who enlisted their elite military training to serve as hired guns for evil ends."
The indictment described Hunter as a contract killer and leader of the group of ex-snipers.
"Three of the defendants were ready, willing and eager to take cold hard cash to commit the cold-blooded murders of a DEA agent and an informant," Bharara said.
Hunter recruited several ex-soldiers in late 2012 and early this year to be a security team for drug traffickers, said the indictment. According to the court papers, the DEA's sources promised Hunter at a March meeting in "an Asian country" (known to be Thailand) that his security team would be protecting thousands of kilos of marijuana and would be seeing "tons of cocaine and millions of dollars."
Audio and video recordings of the meeting show Hunter discussing "bonus jobs" of contract killings, saying the men he had recruited want to do as much "bonus" work as possible, the indictment said.
According to the indictment, Hunter served in the US Army from 1983 to 2004 before becoming a contract killer who successfully arranged several slayings. At one meeting, Hunter was captured on tape describing how he had arranged the killings of real estate agents.
The indictment said a DEA source posing as a drug trafficker in May proposed killing a DEA agent and a boat captain providing information to US law enforcement authorities, saying it was necessary because there was a "leak" within the narcotics trafficking organization.
In an email exchange, Hunter responded: "My guys will handle it. ... Are you talking about both the captain and agent or just the captain?" according to the indictment.
Also charged in the assassination plot were Timothy Vamvakias and Dennis Gogel, a German citizen.
The indictment said Vamvakias served in the US Army from 1991 to 1993 and from 1999 to 2004. He was a sergeant, serving stints in South Korea and later as a military police officer in Puerto Rico.
Gogel was in the German armed forces from 2007 to 2010, attaining the rank of corporal and receiving commendations for his sniper skills, the court papers said. He was deployed for a time in Kosovo.
Two other suspects, Polish citizen Slawomir Soborski, 40, and German citizen Michael Filter, 29, were arrested Wednesday in Estonia where they remain pending extradition to the United States. Soborski was a member of an elite counter-terrorism unit while serving in the Polish armed forces from 1998 to 2002 and from 2003 to 2011. He later worked as a security contractor in Iraq, Afghanistan, Haiti and elsewhere, court papers said. Michael Filter served in the German armed forces from 2006 to 2009.
To carry out the assassination plot, Vamvakias and Gogel offered ideas and plans, including the need for machine guns, cyanide, a grenade, masks and appropriate weapons, the indictment said.
The court papers said Gogel provided the DEA source with two sophisticated latex facemasks that could make the wearer appear to be of another race. The masks were among items Gogel and Vamvakias brought along when they arrived in an African country on Wednesday planning to carry out the murder-for-hire plot, the indictment said.