A US fighter named Russell Bentley who fought with pro-Russian separatists in Ukraine has been killed in occupied Donetsk, Al Jazeera can confirm.

Earlier this month, Russian authorities reported that the 64-year-old citizen of the United States and Russia had gone missing.

Margarita Simonyan, editor-in-chief of the Russia Today news channel and a close confidante of Russian President Vladimir Putin, said on April 19 that Bentley, known as “Texas”, died in Donetsk fighting “for our people”, in an announcement made on X.

Meanwhile, the Vostok Batallion, of which Bentley was a member, carried on Telegram a statement forwarded by the deputy head of the Russian Guard in the self-proclaimed Donetsk People’s Republic, Alexander Khodakovsky, saying that “those who killed Russell Bentley” be dealt with “exemplary punishment”.

The new digital platform Al Jazeera 360 has documented Bentley’s story in a soon-to-air film, A Diary of a Fighter, tracing his journey, transformations, and reasons for choosing to fight alongside Russian forces.

Bentley was known as “Texas” to his fellow separatist fighters.

Here’s all you need to know about the mysterious case of Russell Bentley:

Who was Russell Bentley?

Bentley was raised in Texas in the southwestern US in a wealthy family that was both religious and conservative.

A self-declared communist, he joined Russian forces to fight in Ukraine’s eastern Donbas region in 2014.

Since December 2014, he lived in Petrovsky, Donetsk, with his wife Ludmila, who is native to the eastern Ukrainian region.

He reportedly obtained Russian citizenship in 2021, and last year started working as a correspondent with the pro-Kremlin Russian news agency Sputnik.

Bentley had described himself as a “poet” and had said the US today is “governed by a group of original fascists and oligarchic companies, enemies of Russia and humanity as a whole”.

He said he devoted his life to fighting against them, especially after the US invasions of Afghanistan and Iraq, which he claimed were “based on lies, and their committing crimes against humanity there”.

Al Jazeera’s Awad Joumaa, who directed the upcoming documentary, said: “The film follows the tumultuous life of ‘Texas’, from his birth and upbringing in Texas to a conservative and religious wealthy family, to the developments his country underwent such as the Vietnam War and the assassination of John F. Kennedy. Then, his fighting with the US army, and subsequently his imprisonment for five years for drug trafficking activities. Finally, it explores his arrival in Russia at the end of 2014 to fight, what he called the ‘real evil’ and ‘Nazis of the twenty-first century’.”

Russia often vilifies Ukraine as a country that plays host to Nazi elements, a charge Kyiv and its Western allies say is overplayed by Moscow.

What happened the day he disappeared?

Ludmila Bentley said her husband disappeared on April 8.

She told Al Jazeera that she and her spouse arrived at the Petrovsky Municipal Building in the Donetsk region, controlled by Russian forces, around 3:30pm (12:30 GMT). Upon arrival, they heard reports of casualties from shelling, prompting the fighter to volunteer and help victims.

She opted to wait for him inside the building.

However, when he didn’t return by around 4:15pm, she became concerned.

Witnesses later informed her that a person who was unable to speak Russian fluently and lacked identification papers was abducted. The person was reportedly blindfolded, and restrained before being taken away for reasons that are unknown to her.

Ludmila said that next to their car lay her husband’s phone, which was shattered, along with his hat and glasses.

Unable to locate the car keys, she decided to return the next morning. However, witnesses told her that two individuals in military attire had taken the car prior to her arrival.

Bentley’s recovered bag contained his Russian passport, military ID, driver’s licence, personal bank cards, firearm and carry licence.

Ludmila posted on his Telegram channel, demanding his release, stating he was “kidnapped” by Russian soldiers belonging to a tank battalion.

She said she’s contacted the police, who have opened a criminal case that has been transferred to a “military investigation committee”.

She handed over her husband’s phone after it was repaired, but said she hasn’t heard from the police since.

What’s likely behind this development, as Russia’s war rages on in Ukraine?

According to the Astra Telegram channel, which is run by independent journalists and focuses on developments in and about Russia, Bentley disappeared while filming the aftermath of a Ukrainian attack on a military unit.

Alexander Korobko, a friend of Bentley and producer on the Al Jazeera filming team, said in a Facebook post on April 12 that according to witnesses, Bentley was “taken by people in camouflage”. He suggested they probably mistook him for a spy and took him to military interrogators.

Korobko said he had been in contact with Bentley a few days before his abduction to shoot more scenes with him and his wife.

Except for the ongoing war, he said there was no specific threat surrounding Bentley.

He said Bentley’s death highlights the challenges of enforcing order and law in the Donetsk region, where he was abducted, as it is “one of the grey areas” lacking specific control.

He said that he and everyone who knows Bentley appreciate “his humanitarian work and, most importantly, his military work,” describing him as an “extraordinary personality”.

Both Russian and Ukrainian soldiers have been accused of war crimes throughout the conflict, which has been ongoing since February 24, 2022. Thousands of civilians have been killed, including children, as well as thousands of troops on either side. Parts of Ukraine have also been destroyed.

Officials from Russia, the US and Ukraine do not appear to have officially responded to the case of Bentley.