Police fear a Traveller gang boss may have ordered the arson attack that killed an innocent couple and their two children in Ireland.
Kim English, in her 30s; her husband Philip, in his 50s; and their sons Callum, 12, and Jayden, nine, died when a petrol bomb was thrown into their home early on Tuesday morning in the Birchwood estate, 3km from Waterford city centre.
Philip and Kim's two other children, Nadia, 14, and Elliot, six, remain in a critical condition in hospital.
The gardaí fear a Traveller gang leader may have ordered the deadly attack, local reports claim.
It comes after Philip's son from a previous marriage, John James English, revealed that gangland figures in the city had terrorised his family for years over a £17,000 drug debt owed by someone known to the family.
Only three weeks before the fatal attack, the family car had been targeted with a petrol bomb. Nobody was injured in that incident.
John James also told RTÉ that the home of his mother Anne, Philip's ex-wife, was previously targeted in another petrol bomb attack.
Investigators searching for the killer are believed to be focusing their hunt on three brothers who run a 'low-level drugs operation.'
During police searches, gardaí seized cars as well as phones and other electronic devices.
Philip and Kim English with their children, including Callum, left, and Jayden, centre
Kim and Philip died in the blaze in the early hours of Tuesday morning in the Birchwood estate, 3km from Waterford city centre
Forensic officers at the scene of an overnight fire in the Birchwood estate in Waterford City
Officers are also examining whether a woman drove to the scene with another individual who carried out the attack.
Gardaí, in a statement, said there are people who know who carried out the attack and urged them to come forward.
Security sources explained that officers are fearful that there could be more violence after the attack on the innocent family.
A senior source explained: 'I want there to be no doubt whatsoever here. The people who were killed were completely innocent.
'They were targeted because they knew someone who had owed them money for quite some time.
'The last thing gardaí want to see is more violence, but you've to remember tensions are very high right now. We have so many people grieving, and they're angry, and rightly so.
'But gardaí have seen before how something of this scale can lead to more bloodshed.'
A burnt-out window in the family home in the Birch Avenue
Police at the scene of an overnight fire in the Birchwood estate in Waterford City, Ireland
On Wednesday afternoon, James English, an uncle of Philip, said: 'Well, whoever knows, you'd want to turn up and own up to whoever's done it.
'At the end of the day, we have a lot of the family now wiped out.
'Please, whoever's done it, own up. Be a man and own up for what you have done.'
He said Nadia and Elliot are 'not good' in hospital.
There were emotionally charged scenes at the site of the quadruple murder on Wednesday, with over 100 members of the community releasing balloons in honour of the four victims.
Philip's father Paddy broke down in tears as the song You'll Never Walk Alone played from a car stereo as the balloons drifted skywards.
A vigil was then held in the nearby Sacred Heart Church where hundreds turned out to pay their respects.
Speaking at the balloon release, Philip's ex-wife Anne said they were a happy family.
'I just have no words. I'm lost, and I'm going to be lost without them,' she said.
'She [Kim] is my best friend. We were very, very close. I heard when I got a phone call from one of my family, and I jumped out of my bed.
Floral tributes outside the English family's home
A person holding balloons ahead of a release ceremony to commemorate the lives of a family killed in an arson attack
'Since then, I am numb. I am just shocked. The family is very close. Very happy.'
Ray Power, who is Philip's cousin, urged the younger people of Waterford not to get caught up in the criminal lifestyle.
He described the rampant drug use in the city as a 'demon' which comes into homes and destroys them.
He said: 'You'd be better off going off into a different country, going off and enjoying life, and enjoying yourself instead of looking up to that [dealers], because they'll use you. They don't care about you.'
In the latest Garda statement regarding the murders, a spokesman said: 'The investigation is intense in nature and very active, with multiple searches being carried out across a number of premises in Waterford city yesterday evening.
'A number of electronic devices and vehicles have been seized, which are now subject of technical examination. There have been no arrests at this time.'