When a man with bloodied hands waving a meat cleaver approached a passerby on a London street last week, the natural instinct to flee seemed to have been overwhelmed by a greater need to record the event.

The passerby held his camera phone steady and recorded as the cleaver-wielding man, accused of having hacked to death a British soldier moments before, began a political rant while warning about more violence.

The decision to record the violent incident is just one of a number of examples — ranging from cellphone camera videos of deadly tornadoes, to explosions at Texas fertilizer plants — of people taking what might seem extraordinary risks to document a dangerous event.

"I think in some ways the camera provides a preventive barrier between you and the event which you are recording, and in some ways it sort of removes the person from the element of danger," said Christopher Schneider, assistant professor of sociology at the University of British Columbia, who specializes in crime and social media.

"Because what they're doing basically is paying more attention, focusing and concentrating on the video device and making sure to capture a good video rather than running away because their safety is at risk."

The amateur cameraman in London, who was on his way to a job interview when he came upon the scene of the slain British soldier, said he was never really scared during the time he videotaped the suspect's rant.

"No no, I don't really know these guys," he told Britain's ITV News.

Suspects encouraged passersby to record them

Lee Rigby, an off-duty soldier who had served in Afghanistan, was run over by a vehicle and repeatedly attacked with meat cleavers near his barracks in southeast London. Michael Adebolajo, 28, and Michael Adebowale, 22, are suspected in the killing. The gruesome scene was captured by witnesses' cellphones.

Ed Campbell, senior news editor for ITV News and the first journalist to meet the man and see his cellphone footage, described as "quite a cool customer" in his early 20s.

"He did not seem, to me, to be freaked out by his experience," Campbell said, adding that the man does not want to be identified.

Campbell said that after the killing, the two suspects were actively encouraging passersby who had cameraphones to film them.

"Obviously, most of them were sensible enough not to, but my guy did," Campbell said. "He then began filming the guy at the vicinity of the body. The guy then spots him and starts wandering over to him. At that point you see him flinch slightly then stand his ground as the guy says: 'I'm not going to hurt you, I'm not going to hurt you.' And then starts explaining himself to him."

"He said, 'No no no, it's cool, it's cool, I just want to talk to you,'" the amateur cameraman told ITV News. "And I was continuing to [film]. I was a little bit [scared] to be filming that. After that he was taking time, I was OK and continue to film. He [went] back to the dead body."

The amateur cameraman shot six segments of video, Campbell said, including the immediate aftermath of the police shootout.

"He did not film the police shootout, so he did have enough good sense when the bullets were flying, he put his phone down and he took cover."

An urge to be first

Schneider of UBC said part of the need to capture things on video is that we live in a culture that privileges documentation or record keeping.

"People document things that they see in their everyday lives and then they tell narratives and stories about the things that they've seen. And their way to prove or support the narrative of what it is we're saying — there's evidence.

"I think this would be the case with something that is quite sensational, like witnessing someone being murdered in the street, car accidents, people jumping off of buildings. People are witnessing these things. They record these things, and then when they are telling their story.… they have a video of it and this supports what they're saying."

With so many outlets for the dissemination of that evidence, there's an urgency to be the first person to upload it on Facebook or YouTube to support the things people are seeing, Schneider said.

"If you can put that video online before anyone else, this is going to show that you are there [and] it's going to be picked up I think and circulated by other news media and discussed by other the news media. In this way, it sort of spotlights the person who recorded the event. And we've seen in some circumstances where those people become kind of web celebrities.

"People like being paid attention to and this ... may be an explanation why someone may stand around and record while someone is being murdered."

With files from The Associated Press