(CNN) A former US soldier described as a "ringleader of trained assassins" is facing life in jail after being found guilty Wednesday of organizing the killing of a woman in the Philippines in 2012 for cash.

Former US sniper instructor Joseph Hunter, nicknamed "Rambo," was convicted along with two other men in a New York court Wednesday of conspiring to kidnap and murder as part of a murder-for-hire scheme following a 12-day trial.

Hunter, who for years worked as a soldier of fortune, is already serving a 20-year sentence over a range of charges, including the attempted murder of a US drug enforcement agent.

Speaking after the verdict, US Attorney Geoffrey Berman described the case in a statement as "horrifying," with details "usually seen in action movies."

"(These men) conspired to end the lives of people overseas whom they had never met. Today a unanimous jury convicted them for their craven indifference to human life," he said.

Sentencing for the three men, US citizens Hunter, 52, Adam Samia, 43, and Carl David Stillwell, 50, will take place in September, with a maximum penalty of life in prison.

Hunter was a former US army sergeant who left the armed forces in 2004 after more than 20 years, while Samia has previously claimed to have worked as a "contractor" for clients in the Philippines, China, Papua New Guinea and the Democratic Republic of the Congo. All three men had extensive firearms training.

According to a statement by the United States Attorney's Office, the three men agreed in 2011 and 2012 to commit a number of murders across the world in exchange for a salary, including "bonus payments" for each victim.

In early 2012, Samia and Stillwell traveled to the Philippines where Hunter gave them information on their victims and weapons to use in the killing.

After watching their female Filipino target for months, the two men murdered her by shooting her in the face multiple times then dumped her body on a pile of garbage.

She was found there later by local authorities. Both Samia and Stillwell were paid $35,000 by Hunter for killing the woman.

The investigation into the three men was an international effort, bringing together US law enforcement agencies with the Royal Thai Police and the Philippines National Police.

This prosecution is being handled by the US Attorney's office Terrorism and International Narcotics Unit.

'Ringleader of trained assassins'

It isn't Hunter's first time in a US court -- the former US soldier was sentenced to 20 years in February 2015 over the planned killing of a US Drug Enforcement Agency (DEA) agent, as well as a DEA informant.

In statement released following the trial, US Attorney Preet Bharara described Hunter as "an admitted contract killer, convicted drug trafficker, and ringleader of trained assassins."

"Hunter and his cohorts turned from serving their countries as soldiers to becoming mercenaries for hire, plotting to kill a DEA agent and informant and trafficking in massive quantities of cocaine," the attorney said.

In 2013, Hunter hired a group of four former soldiers from the US, German and Polish armed forces to act as bodyguards and hitmen for what they thought were a Colombian drug cartel, according to the US Attorney's Department.

In fact, the men who recruited the former US soldier to protect their cartel were "confidential sources for the DEA," the indictment said at the time.

In March 2013, Hunter described his work to one of his teams of contractors as "like a military mission," according to the US Attorney's Office.

"You know, you see everything. You see James Bond in the movie and you're saying, 'Oh, I can do that.' Well, you're gonna do it now," he told the team.

In a recorded meeting, Hunter claimed he'd taken part in weapons trafficking and used grenades to carry out an attack.