The Irish Examiner obtained the video on Wednesday evening as Government continued to face questions over why officers were not present at the event and why it took them so long to respond.
The footage, which lasts for one minute and was taken on a mobile phone by a shocked bystander, shows Mr Byrne's bloodied body lying motionless beside the counter at the entrance of the hotel.
Locals attending the event then go outside, where they see a silver van slowly driving away.
"There's no way they're guards," one person is heard to say, while another shouts: "They're not cops, jeez, look at that young fella, they're not guards."
The person videoing the scenes then zooms in on the van, saying "they're stuck down with the yoke, they're trying to get out down there", in what is believed to be a reference to the hotel gates.
The situation is likely to lead to fresh questions about why it took gardai so long to arrive.
However, despite ongoing opposition criticism of what happened, at separate general election events on Wednesday both Taoiseach Enda Kenny and Tánaiste Joan Burton expressed "full confidence" in garda commissioner Nóirín O'Sullivan.
The Fine Gael leader saying he hoped the new high visibility policing unit set up in response to fears of a gangland war in the capital by his party colleague Justice Minister Frances Fitzgerald would "yield results", while Ms Burton said the "saturation" garda response is required.
However, Fianna Fáil justice spokesman Niall Collins claimed the plans are just "repackaged" and involve taking officers from other less high-profile areas - putting additional pressure on other parts of the job.