ON Boxing Day last year, father-of-four Robert was in the kitchen with his partner Natasha when three masked gunmen broke into his house in the dead of night and struck him in the back of his head with a hammer.

Natasha and their children were ordered into the living room while Robert was 'kneecapped' - shot twice in his knees and twice in the ankles - by thugs who were working as part of an illegal paramilitary group.

He's one of dozens of victims who have been targeted by vigilante gangs in Northern Ireland and left crippled by kneecapping - a violent act that was popular during The Troubles, a 30-year period of political unrest between the Protestants and Catholics.

During this time, militarised groups such as the IRA saw themselves as law enforcers in their own areas.

They went after people they believed were damaging the community, including drug dealers and child molesters.

But 20 years after the Good Friday peace agreement was signed, revenge attacks by new paramilitary groups are still happening in residential areas in Belfast with alarming regularity - and many of the targets are boys as young as 16.

A new BBC documentary, Shot by my Neighbour, sees investigative journalist Stacey Dooley - who is also taking part in the latest series of Strictly Come Dancing - travel to the Northern Irish capital to speak to victims of kneecapping attacks and those who carry them out.

Shot for joyriding
Today, in Belfast, kneecapping is still used as a punishment for anti-social behaviour such as joyriding - and police are powerless to stop it.

The neighbourhood paramilitary groups are highly influential - and with many Northern Irish people distrusting the police following The Troubles, the local community will often turn these rogue law enforcers to 'keep the peace'.

There is no phone number or website to contact the violent vigilante groups to report antisocial crime - residents know who members are by their reputations, and there's a member on almost every street.

People accused of crime are reported to members and are then at risk of being shot by their neighbours.

The alleged offenders are given 'an appointment' via an anonymous text from the paramilitary groups and are asked to go to a certain place at a specific time.

At these violent 'appointments', victims are shot the kneecaps - and sometimes ankles elbows in what's known as a 'six-pack' if the group deems the offence to be particularly bad.

They are threatened with even worse violence if they don't turn up - and there have been reports of parents taking their children to the thugs in a bid to negotiate a less severe 'punishment'.

Teenage boys fearing for their lives
Last year, 73 people were beaten up in revenge attacks by paramilitary groups, while 28 where shot.

Stacey meets two of them - teenage boys who have fallen foul of the local paramilitary due to their antisocial behaviour on their Belfast estate.

John*, who has his face obscured and his voice changed as he's frightened of rebuttals, says he received an appointment to be shot at a certain time.

"I had a few pints, then went to see the guy," says John. "He kept telling me he'd 'look after me', and would only used a hand-sized gun to shoot me.

"I did bad sh*t, and I'll accept it. But I was punished by the law then I was shot four times."

Another young man, who has had 70 convictions for antisocial behaviour, received his first threat at the age of 16, and has had three threats since then.

He tells Stacey he is on medication for PTSD as he is constantly fearful of attacks.

Stephen, who runs a youth club on the Divis Estate, a Catholic working class area of the city plagued by drug and anti-social behaviour problems, says four kids have been shot there recently.

"Luckily, they all survived, but they are all damaged for a long time. One of them was shot four times," says Stephen.

"There were younger kids playing nearby when it happened, and everyone ran. A woman had to use tampons from her handbag to stop the blood flow.

"How does doing this stop crimes or change anything?"

Just like shooting a 'parasite'
Stacey manages to set up a meeting with a local paramilitary group, to find out why they believe their vigilante justice is still necessary.

The group are incredibly secretive, banning Stacey from taking her phone with her and making her travel to the meeting in a van with boarded-up windows.

Speaking to one of the men, who is wearing a balaclava and flanked by two colleagues wielding rifles, she asks them why they do it.

"We don’t feel guilt or remorse, we are sticking up for the wider members of the community and help people," he says.

"If you have to shoot somebody to help people, then we do it. We are hurting a parasite."

"We see this as a justified and measured response - we don't live in a normal society and this is how we deal with stuff.

"We're normal men. We could be living next door to your grandmother, and that’s why people fear us, because we come out of the shadows, do our deed, then go home."