George Gonzaga Bento (36) was last week found not guilty of any offence by a jury at the Central Criminal Court in relation to the fatal stabbing. Security sources said Mr Bento now planned to return to his native Brazil.
The family of the teenager are planning to hold a demonstration in Dublin over what they say is the lack of justice over Josh’s death.
Sources said gardaí will discreetly police the event to ensure it passes off peacefully amid rising tension.
“There are issues online with a lot of abuse being levelled at both the bereaved family and Mr Bento. This is entirely unacceptable and it is making this situation even more fraught,” a source said.
“There are garda concerns that this online abuse and harassment could translate into violence on the street, which is something we want to avoid at all costs.”
The source said there were “no winners” in the aftermath of Mr Bento’s acquittal, and it was “a priority” for gardaí on the northside of Dublin city to ensure “racial tensions do not now soar” in the community.
Josh’s sister, Jade Dunne, spoke in recent days about the online vitriol aimed at her family in the aftermath of the trial.
“We have received an awful amount of abuse since the verdict. I’m deleting all the horrible comments once I see them, but they’re coming back just as fast. There were so many racist comments from people who were saying that Josh deserved what happened to him,” she said.
On Tuesday, the jury accepted Mr Bento was acting in self-defence after being attacked by a gang when he and a colleague tried to retrieve a stolen bike. He said he had pulled out a utility knife he carried for cutting fruit and stabbed three people, including 16-year-old Josh.
They rejected the State’s contention that Mr Bento had decided to take the law into his own hands, had exaggerated the threat posed by his attackers and knew at the time the force he used was not necessary to repel the attack.
He had been in custody for more than 16 months, having been refused bail by the High Court. Following the verdict, Mr Justice Paul Burns told him he was free to go. Outside court, Mr Bento said “I’m sorry” and asked for forgiveness from Josh’s family.
On Facebook, the teenager’s mother, Diane Dunne, thanked everyone for “their kind words, but I’m not going down easy — I’ll keep fighting for Josh until the day I die”.
Jade Dunne said: “We’re now planning to stage a protest in Dublin with banners and pictures of Josh just to keep his story and our fight for justice alive — it’s the only way we can keep this movement going.”