In the spring of 2015, former U.S. soldier Craig Lang traveled to Ukraine and joined a paramilitary group fighting the Russians.

“I never noticed any fear,” said Mamuka Mamulashvili, who commanded Lang in the Georgian Legion.

Four years later, Lang is under house arrest in Ukraine. His situation has nothing to do with his conduct inside the eastern European country. Lang is facing charges in the U.S. for allegedly killing a Florida couple during a stint back home last year.

His fate remains unclear.

The U.S. has requested Lang’s extradition, but Ukraine has yet to hand him over. In a letter to his attorney obtained by NBC News, Ukraine’s national prosecutor’s office said it has reached out to the Justice Department asking that American authorities promise not to impose the death penalty on Lang.

The request marks the latest twist in a bizarre and bloody saga that’s now playing out in a country at the heart of the impeachment proceedings against President Donald Trump.

Experts say the case has the potential to strain the already fragile relationship between the U.S. and Ukraine.

“This is expected to be a very difficult case,” said Stanislav Batryn, a prominent lawyer and human rights advocate in Ukraine. “It becomes part of a political game between the two countries.”

Both the State Department and the Justice Department declined to comment.

Requests like the one from Ukraine’s national prosecutor’s office are not uncommon, international law experts say, especially for European countries that have signed a treaty to abolish the death penalty.

But unlike most European nations, Ukraine has no extradition treaty with the U.S. The case is further complicated by the dueling visions of Lang in the U.S. and Ukraine.

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U.S. law enforcement officials describe Lang as an “absolutely heartless” criminal who, along with another ex-U.S. soldier, robbed and fatally shot a middle-age couple 18 times in April 2018. He has spent the past five years as a mercenary globetrotting among armed conflicts in Africa, South America and Europe. And in addition to the double murder, he has been charged with passport fraud and named in federal court documents as a mentor to​ an Army soldier​ arrested for allegedly plotting to bomb U.S. news stations.

But in Ukraine, Lang is known as a brave warrior who spent years defending Ukrainian sovereignty in a brutal war against Russian-backed separatists. He is a paramedic, an English teacher and a newlywed husband whose Ukrainian wife is six months pregnant.

“We know that in the U.S, he is very negative person in mass media,” said Dmitry Morgun, Lang’s defense lawyer. “In Ukraine, he is not. In Ukraine, he was a hero. He defends our interests and our country.”

Anna Osipovich and Craig Lang embrace during Lang's hearing in Vinnytsia. The couple were married the morning before the hearing. Vezha

An Army soldier turned international fugitive

A native of North Carolina, Lang joined the Army at 18, serving in Iraq and Afghanistan. The Army discharged him six and a half years later, after he went AWOL and drove from Texas to North Carolina with his military equipment, telling people he wanted to murder his wife, the Ayden police chief told local news outlets.

"I told my commanders repeatedly that I was going to murder her," Lang would later tell VICE in Ukraine. "The motherf------ thought I was bluffing."

The following spring, he flew to Ukraine to join a paramilitary militia called the Right Sector, according to his testimony in Ukrainian court.

He’s not the only U.S. citizen drawn to Ukraine's war. Ultranationalist battalions like the Right Sector​ have become a destination for other former American soldiers with far-right political leanings​.

In Ukraine, Lang would link up with Alex Zwiefelhofer, then a 19-year-old from Wisconsin who had deserted the U.S. Army to become a foreign fighter, first in France and then in Ukraine. Zwiefelhofer is now implicated in the Florida killings alongside Lang, according to U.S. law enforcement.

In between his stints with the Right Sector, Lang fought with the Georgian Legion, an anti-Russia militia that has fought alongside the Ukrainian army.

Lang served on contract with Ukraine's Army with the Georgian Legion and with a volunteer far-right paramilitary militia called the Right Sector. via Facebok

Lang and Zwiefelhofer left the Right Sector together ​for South Sudan in 2017, in hopes of fighting al-Shabbab, a Qaeda affiliate based in East Africa, court documents say. But Sudanese officials denied them entry and sent them back to Kenya to obtain the proper visas.

They were deported from Kenya shortly afterward. Lang’s passport was canceled, due to unpaid child support, prosecutors say. Zwiefelhofer was booked into jail for sexual exploitation of a minor almost immediately after landing in the airport in Charlotte, North Carolina, after airport Customs officers found incriminating videos on his cellphone, according to the complaint. He was released on bond and then left the state.

In February and March 2018, Lang and Zwiefelhofer chatted online about Venezuela — specifically, about their intentions to join military-like raids, fight against the Venezuelan government and “kill people,” according to the indictment. They formulated a plan to travel to Florida, the complaint says, and discussed hot-wiring and stealing a yacht, potentially killing a yacht owner and smuggling firearms to “South America or Ukraine.”

Lang and Zwiefelhofer were set on going overseas to fight alongside the Venezuelan resistance, federal prosecutors say, but they needed money.

The pair checked into a Miami La Quinta Inn on April 5, according to the complaint. They posted selfies in tropical shirts and then typed out a listing on the website Armslist.com, offering 15 firearms including Glock handguns and one high-powered rifle.

The ad caught the attention of Serafin Lorenzo, 53, who often “flipped” property for profit, court documents say. "I have cash on hand," Lorenzo wrote, offering to pay $3,000 for the haul of weapons. "Mine is a sure deal."

Late on the night of April 9, 2018, Lorenzo and his wife, Deana, 51, drove roughly three and a half hours to complete the sale in Lee County, Florida. Police found their bullet-riddled bodies the next morning, inside their car parked in a church parking lot.

Serafin Lorenzo was shot 11 times in the head, neck and abdomen. Deana was shot seven times, mostly in the head and body.

Investigators didn’t find any cash at the scene. They did, however, find Serafin’s cellphone​. ​It showed recent texts with the Armslist seller, who was using a Walmart burner SIM card. Investigators later traced the SIM card to Zwiefelhofer’s cellphone, according to the complaint.

A search of Zwiefelhofer’s Google and Facebook histories showed he was traveling with Lang in Miami, court documents say. During that time, he searched phrases like “Classified Miami Handguns,” “Hotwire Boat Ignition Switch,” and “How to Smuggle Myself to South America.”

He also repeatedly searched for a movie scene where subjects in a vehicle are ambushed by multiple shooters — an ambush that resembles the killing of the Lorenzos, court documents say. One of Lang’s associates would later tell investigators that Lang said he “gunned down some people in Miami” with “some guy who is from Wisconsin” after they “unloaded both of their clips into the ‘dude’s’ red truck," according to the criminal complaint.

Authorities arrested Zwiefelhofer in Wisconsin in May, after he was caught lying on a gun purchase form. Like Lang, Zwiefelhofer denies killing the Lorenzos. When interviewed in May, he told authorities he had left Miami after he and Lang ran out of money. They stayed in a dog park overnight, he told investigators, and the sprinkler system ruined his phone. According to the complaint, Zwiefelhofer’s father recalled him saying his trip to Venezuela’s armed conflict didn’t work out because the boat captain was murdered.

A photo from Alex Zwiefelhofer's Instagram feed, posted a month before authorities arrested him in May. via Instagram

When the FBI searched Zwiefelhofer’s home, court documents say, they determined his laptop was used to create the online gun posting. It also had accessed a fake Facebook profile for “Jeremy Goldstein” — the fake name of the seller whom Serafin Lorenzo believed he was meeting.

Zwiefelhofer has pleaded not guilty; his lawyer did not return a request for comment.

Lang, meanwhile, was long gone. A federal indictment in North Carolina says he applied for a passport in September 2018 using another man’s identity, which he paid for with $1,500 cash and a suitcase filled with five firearms and a grenade in a Walmart parking lot. Court documents related to a separate felony indictment in Arizona say Lang used his restricted passport to cross into Mexico two and a half weeks later, after he put a black ink stain over the stamp limiting his travel.

Court documents say he then traveled to Colombia, near a rumored mountain safe house for Venezuelan resistance fighters, and then to Spain two months later. Using social media, investigators eventually placed him in Ukraine.

A 16-month manhunt ended in August when he was arrested at a Ukraine-Moldova border checkpoint. Lang and Zwiefelhofer were indicted for the Florida murders in September.

By then, the authorities in Florida were itching to prosecute Lang.

“We take this very personally,” said Lee County Sheriff Carmine Marceno. “If you commit a crime in this county, you can run. You can't hide. We are going to find you. You're coming back. You're going behind bars.”

A Ukrainian war volunteer turned cause célèbre

In Ukraine, Lang has a different reputation: a well-trained asset for an under-resourced army.

The conflict between Russia and Ukraine has claimed 13,000 lives, including over 3,000 civilians. Nearly six years have passed since Russia’s annexation of Crimea drew wide condemnation from the international community.

Today, some Ukrainians feel “abandoned” by the West, says Igor Skritsky, a soldier who is friends with Lang. Foreign volunteers like Lang earn admiration in Ukraine, including a simplified path to citizenship under a recent law. The asylum process takes foreign participation in the war into account, Ukraine’s migration agency said in an email to NBC News.

“We all respect people who came here to fight for Ukraine,” said Batryn, the Ukrainian human rights advocate. “We are united fighting for values we gained after the revolution, for principles created by Americans.”

Lang defended Ukraine’s front line, a hundred meters from the enemy, said Mamulashvili, Lang’s former commander. The unit subsisted on buckwheat and fish cans, he said, sleeping in trenches dug into a barren field. Lang was “very friendly” and “never had problems with other soldiers.”

A photo of Craig Lang posted on his Instagram feed from April 2019 in Ukraine. Faces obscured by NBC News. via Instagram

“I really was very surprised when they told me he killed those civilians,” Mamulashvili said. “We are always talking about helping Ukrainian civilians near the front lines. I never thought he could do this.”

Lang’s extradition trial has not been scheduled yet. He has, however, gone to court four times for a Ukrainian version of a bail hearing, where a city judge decides whether he must continue to wait for trial in jail.

Those hearings have not gone smoothly. ​A series of snafus have bogged them down, including the arrival of thick stacks of U.S. State Department documents with no Ukrainian translations. ​In just the past four months, Lang has been jailed, released on house arrest, jailed again and released on house arrest yet again.

In recent hearings, Lang has used his service in Ukraine’s war to appeal to the court and the media.

“We still have a war going on,” Lang testified at the appeal hearing. “There are people that are still dying. There are people that still need help. And I wanted to help.”

Lang is also attempting to get refugee status in Ukraine. In his asylum application, he claims he needs protection because President Donald Trump “has very close ties and a relationship with Vladimir Putin” and is working “at the request of the Russian government” to target foreign fighters for Ukraine.

In arguing against his extradition, Lang’s lawyers emphasized the possibility that he could face the death penalty in the U.S., which clashes with Ukraine’s legal obligations to European human rights treaties.

The national prosecutor’s office appears to agree. In a letter to Lang’s lawyers, the office said it asked the U.S. to guarantee Lang “would not be punished by a death sentence” and “be brought to justice only for the crimes for which he is being extradited.”

U.S. prosecutors in Florida declined to comment on the case. But last week, they filed a superseding indictment with new charges: violation of the Neutrality Act and conspiracy to kill, kidnap or maim persons in a foreign country, based on evidence that the duo was trying to fund a military expedition against Venezuela’s government.

Ukrainian legal experts say his extradition trial is unlikely to begin until the nations resolve loose ends like Lang’s asylum claim and the death penalty. That could take years.

“I just hope that we can be happy, and that this little one will have full family with a father and mother,” said Anna Osipovich, Lang’s fiancée, referring to her unborn child. “It seems like no one is caring about his human rights.”

For some in Ukraine, Lang is emerging as a martyr for a court system that critics say is infested with U.S. political influence. But in Lee County, Florida, the scar of his alleged crimes remain unhealed.

“It’s a roller coaster when you want something this badly,” said Lee County Detective Sarah Rodriguez, who has investigated the case since the initial crime scene. “We want people to answer for what they’ve done.”

Rodriguez says she has poured thousands of hours into the case and struggles to stop thinking about it. For the last year and a half, she has also been providing updates on the case to the Lorenzos’ loved ones.

“There’s uncertainty now,” she said. “I do believe everybody gets their day. I just pray it all works out for us.”