A murder victim’s father has called it “appalling” that a YouTube video remained online for months after it helped fuel a gang rivalry that led to his 15-year-old son’s death.

Jermaine Goupall was fatally stabbed near his home in Thornton Heath, south London, in August last year by members of a gang who had gone to the area to target a rival group.

Police believe Goupall, who was stabbed in the thigh and bled to death on the evening of August 8, did not belong to either gang and was targeted by chance.

The gangs had been both taunting each other online in YouTube music videos.

The Government is due to publish its Serious Violence Strategy on Monday which is expected to announce measures to crack down on violent groups’ use of social media, against a backdrop of violence in London in recent days.

The Met on Friday dismissed claims it has “lost control” of city streets as it announced that 300 extra police officers would patrol violent-crime hotspots this weekend. Stop and search would be further utilised to stop further attacks, Commissioner Cressida Dick said.  

The circumstances of the attack on Goupall had been predicted in lyrics in a video, written by one of the defendants, Junior Simpson, aka M-Trap 0, his trial heard.

Some of the videos were played to jurors and showed Simpson boasting about stabbing someone with a “shank”.

Local newspaper the Croydon Advertiser reported the videos shown to the jury were still online last month, but reported on Friday that one had been removed, just after HuffPost asked YouTube why it was still live.

Jermaine’s father Stanley told HuffPost it was “appalling” the video remained online eight months after his son’s death, adding it led him to question the company’s stated commitment to removing clips that incite violence.

“That music has caused a death… The artist [behind the video] has been criminalised for his actions… That’s quite appalling. YouTube should be held a little bit responsible for keeping it up,” he said.

“Someone who’s been convicted of murder, who’s actually talking murder on the video… It shouldn’t be allowed… Everything that video said it was gonna do, it was done.”

HuffPost asked YouTube why it took so long to remove the video but had not received a response when this article went live. 

Stanley Gouppall added he was frustrated no one from YouTube had reached out to his family, despite the company previously saying their “hearts go out” to them in statements to the media.

Gouppall said: “A person should have come to us… They have not done that.

“Just to say ‘we’re sorry, we weren’t fully aware of what was going on’.

“They haven’t put nothing in writing to us. I feel really low that they’ve not come to us.”

Met Commissioner Cressida Dick said last week that social media could be fuelling the rise in knife crime.

“There’s definitely something about the impact of social media in terms of people being able to go from slightly angry with each other to ‘fight’ very quickly,” she told The Times.

Police told HuffPost they had been monitoring “a number of videos that incite violence” since September 2015.

“The gangs try to out-rival each other with the filming and content – what looks like a music video can actually contain explicit language with gangs threatening each other,” temporary Detective Superintendent Mike West, from the Metropolitan Police’s Operation Trident anti-gang mission, said.

“There are gestures of violence, with hand signals suggesting they are firing weapons and graphic descriptions of what they would do to each other.”

He added the force had indexed more than 1,000 videos and takes action against individuals in them “where we can”.

West said police could respond by obtaining criminal behaviour orders at court, which can forbid people from associating with certain people, entering certain areas, wearing hoodies, having unregistered mobile phones or making “contributions to websites”.

He added: “We only ask for videos to be removed which we believe raise the risk of violence.

“We have been working with Google to take down some of the videos which they have done after approaches from us, but as with all serious violence, there is always more work to be done and we continue to work in partnership with them.”

In a focus group on the issue of violence and social media in 2016, young people described “shootings and stabbings” in response to mocking music videos being uploaded, as “people from other ends have got to retaliate”.

One person said there were “some serious problems” when a gang attacked another estate.

“Over the course of a week there were a number of different stabbings and shots fired as a result of a couple of videos they put up against each other as one video goes up and then a response video and so forth, it just raises the tension and makes things happen probably a lot quicker,” one young person said.

Another young person said: “If you go on Twitter you can see these videos all the time. People are basically calling each other out, so obviously it’s causing reactions.”

This week, an 18-year-old was imprisoned for possession of a firearm and drugs offences after police saw him posing in an Instagram video with a balaclava, rapping and and posing with a shotgun and a handgun.

Carl Brown was sentenced to three years in prison after police found a shortened single-barrelled 12 Bore shotgun, ammunition, heroin and cocaine at his address in Thornton Heath, where Goupall also lived.

“We know that social media can be used to incite violence and we will continue to take action against the people that take part in this behaviour,” Detective Constable Peter Whibley said after Brown’s sentencing.