As the cameraman marches towards him, a gravelly voice orders him to roll over and he obliges, moaning with pain.
"Say long live (Gaddafi)!... Say long live Muammar!" the voice shouts.
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"Allahu Akbar," he replies. God is greatest. Shots ring out, and the camera jerks away and goes dark.
Another online clip, less widely seen, shows Gheriani's unmoving body laid out on the back of a pick-up truck, surrounded by what appear to be grinning militiamen.
They have circulated widely in this rebel stronghold, where Libyans hail Gheriani's defiance and see in his tormentors the familiar brutality of the four-decade-old regime they have been struggling to overthrow since February.
But his family and friends back home do not know whether he was killed or taken prisoner by Gaddafi's forces.
"When I saw the tape, I could not move for 24 hours," his older brother Abdullah, 40, says. "I didn't eat, I didn't drink, I didn't sleep."
They believe he was shot on March 6, a day after he headed to the front, unarmed, to help evacuate the wounded from the front lines.
They describe the heavy-set and bespectacled 38-year-old as an intelligent, cheerful, kind-hearted friend and neighbour, who had little interest in politics and no experience of war prior to the February 17 revolution.
The uprising against Gaddafi began with mass protests across the country inspired by the demonstrations that toppled regimes in Tunisia and Egypt, but soon escalated into a civil war that has split the country in half.
Khaled al-Fazzani, a close friend, said Gheriani cried when he saw the early images of bloodied protesters in mobile phone videos broadcast on satellite TV, clips that would eerily foreshadow his own.
"He said 'I have to go. I have to defend people against this oppression,'" Fazzani recalls. "I told him there are planes and tanks and rockets. You have nothing, you can't fight them. He just said he had to go."
The two grew up together in the small town of Al-Marj, in the verdant hills north of Benghazi where the sea breeze ripples through fields of wildflowers.
They watched football together, with Gheriani rooting for Real Madrid and Fazzani cheering on Barcelona.
"We played against each other, but Ahmed always won. He always won in everything," Fazzani says.
Muslim piety runs deep in this rural village, and Fazzani says he had mixed feelings when he saw the clip of his best friend bleeding on the asphalt.
"I was proud of him because he said 'There is no god but God,' but sad because he was lying there all alone."
Gheriani's older brother Yusef also expresses pride in the testament of faith, but his eyes turn red and fill with tears when he describes it.
Ahmed Gheriani is one of more than 400 Libyans from the eastern part of the country who have gone missing since the start of the uprising, according to the Libyan Red Crescent, which keeps detailed records.
The group is unable to say, however, who has been arrested and who has been killed, and it has no contact with Gaddafi's government.
"When they get arrested, they are just gone. Maybe they will call their family or something, but in general nobody knows," says Dina Jarbou, a Red Crescent volunteer.
The rebels' leadership council assumes Gheriani was killed by his captors.
"We presume he is dead, because Gaddafi's thugs do that well," says spokesman Mustafa Gheriani, a distant relation. "They don't take prisoners."
He declines to hold up Gheriani as a symbol of the revolution because he fears it might take away from other stories of self-sacrifice.
"This is the time when heroes abound," he says.
The clip of the shooting, which can be viewed at www.youtube.com/watch?v=BLXA4lGiOR8, has received more than 32,000 hits.
Ahmed's bed is still unmade in the small room where he lived in his extended family's house. Down the hall is a larger, unfinished room with pink wallpaper where he was planning to move once he got married.
Friends and family said he hoped to wed this summer but had not yet found the right girl.
"I asked him before he left: 'Shouldn't you get married before you go off to war?" Fazzani says.
"He said: 'I'll get married in heaven.'"
