O'Brien was found guilty of murdering 21-year-old Josh in an act of "pitiless savagery" today after an international manhunt brought him to justice.
He fled the country on a private jet in 2015 after calmly walking out of RE Bar in Hillingdon and arranging the flight to the Netherlands.
The 31-year-old grew his long hair and a beard and got the tattoo of his child's name covered over as he used false identity documents to travel to countries including Germany, Belgium and the Czech Republic.
The CCTV footage released today shows O'Brien walk up to Josh in the busy bar with the knife in his right hand.
O'Brien then slashes Josh's neck at speed before people run away in terror as blood gushes from the wound.
He is then seen coolly walking out of the bar with his hands in his jacket pockets.
The video also shows O'Brien visit an Indian restaurant and go clothes shopping in Ashford, Kent after the horrific murder.
Friends helped the boxing and martial arts fan avoid authorities after he was added to both Europol and Interpol's most wanted lists, the Old Bailey heard.
O'Brien tried to claim he had felt threatened by Mr Hanson's "very aggressive body language", saying he felt the roads planner was "ready to attack me" and may have been armed.
At bar closing time, he approached Mr Hanson, asking him "what's your problem?" before pulling the knife from a pocket of his expensive Canada Goose jacket and fatally slashing his victim.
O'Brien claimed he wanted only to "pretend to attack" Mr Hanson with the blade to "scare him", adding: "From the bottom of my heart, I did not mean to touch him with that blade."
But jurors saw through his lies and convicted him of murder after 55 minutes of deliberations.
He will be sentenced by judge Nigel Lickley QC on October 17.
After an international manhunt O'Brien was finally arrested in Romania on March 23 this year and brought back to Britain on April 5.