Shortly after being zapped, Robert Dziekanski, 40, died.
The video is causing international outrage, and the man who took it, fellow traveler Paul Pritchard, 25, of Victoria, British Columbia, spoke exclusively with The Early Show co-anchor Hannah Storm about the Oct. 14 incident Friday.
He called it "shocking" and "disgusting."
The video shows the man screaming and writhing in pain on the floor shortly before he dies.
Four Royal Canadian Mounted Police converged on Dziekanski, who couldn't speak English and who had languished in the airport arrivals area for 10 hours after his flight arrived. It was the first time he'd been on a plane.
Dziekanski had been waiting for his mother, who told him to wait in the baggage area. But she couldn't get in there, couldn't get a message to him, and finally went home after being told he never arrived.
On the video, a bystander tried to calm Dziekanski down, but he didn't understand. Then, he picked up a computer and threw it, then tossed a piece of furniture.
Dziekanski appeared calm when the police arrived.
The video shows him backing up, raising his hands and turning away before the police stun him with the 50,000-volt Taser, sending him to the floor screaming before he's stunned again and the Mounties pin down his head and limbs to handcuff him.
Pritchard told Storm it was the Mounties themselves who first made him realize the video, which they'd confiscated, might be worth retrieving, and publicizing.
He says he was motivated by "the fact that the police actually took it from me and didn't give it back, and, you know, broke a verbal agreement, promising to give it back, and they took it away. (That) led me to believe that maybe there's something important on that footage that I needed to get out to the public."
Pritchard says that, when the incident began, Dziekanski "was acting a little bit strange. He was banging on glass. He was actually trying to get back into the secured area.
"I woke up, and started watching. And as soon as he got back through the glass doors, that's when I started rolling with the film.
The Mounties took half-an-hour just to show up, Pritchard said, and "When police arrived, he stopped everything. He put up his hands. He gave up. When the police came, he thought it was over. The Mounties did not see him at this point break anything."
Why did they taser him?
"I have no idea," Pritchard responded. "It was the first step they took."
They tasered Dziekanski at least twice, Pritchard said, adding that after the first time, "There's audio of the man saying, 'Hit him again, hit him again' when he's on the ground.
"He was on the ground. There were three officers on him, then the officer says, 'Hit him again, hit him again.'
"One officer took his one knee and leg and kneeled on his neck and head. Unfortunately that's when he stopped -- he lost consciousness.
"He was screaming. He was shaking a bit. Then all of a sudden, his body went limp.
"It was shocking. It was disgusting."
A police timeline shows it took four minutes for the Mounties to call for medical assistance, and it was 12 minutes in all until help arrived.
"We didn't know what was going on," Pritchard recalled for Storm. "We were watching. And I stopped filming. We didn't know what to do. We heard someone say, 'Code red, and go call medics.' And you see someone check his pulse, but nobody gave him medical attention. But, as soon as the medics arrived, they ripped off his shirt, put in a mouthpiece, and right away started administering CPR."
When asked by Storm what he would say to Dziekanski's mother, he replied, "Apology, you know, as a Canadian -- we apologize. For everybody."
Pritchard says he believes his video recording will contribute to changes in police tactics in Canada when it comes to use of force.
The video has made its way around the world via the Internet and international newscasts, and prompted a flood of criticism of police.
Poland's ambassador to Canada, Piotr Ogrodzinski, says he was shocked by the video, adding it appears the police action was unsuitable and Poland wants some immediate answers.
RCMP Cpl. Dale Carr says he's been getting angry calls from people, but says they're coming to conclusions based on one piece of evidence and not waiting for all the evidence to come out. He says that won't happen until an inquest is held.