IT took just £1.50 worth of petrol, bought just half an hour beforehand from a Farnworth petrol station, to kill four innocent children, severely injure their mother and devastate a family.

On December 11 last year Zak Bolland, David Worrall and Courtney Brierley decided to escalate the ongoing feud they were involved in with the Pearson family by fire bombing their terraced Jackson Street, Walkden, home.

Bollland, aged 23, and 26-year-old Worrall prepared for their terrible crime by visiting the BP petrol station on Longcauseway, Farnworth.

They were captured on CCTV filling a petrol can with just £1.50 worth of fuel and using it to fill three or four empty bottles left over from alcohol they had bought to drink with others earlier in the evening.

The pair, encouraged by Bolland’s girlfriend, 20-year-old Brierley, then sneaked around the back of the Pearsons' home just before 5am.

A jury was shown CCTV, taken from a neighbour’s camera, of them lifting out a fence panel, creeping into the garden and then two bright flashes as petrol bombs thrown into the house exploded.

Seconds later Bolland and Worrall ran from the garden, down an alleyway to nearby Alexandra Road where Brierley was waiting in a car.

Inside the house Michelle Pearson, her children, 15-year-old Demi, Brandon, aged eight, Lacie, aged seven and three-year-old Lia as well as her son, Kyle Pearson, and his friend, Bobby Harris, both 16, had been sleeping, unaware of the killers outside.

Bolland and Worrall, who had been armed with a machete and an axe, smashed the kitchen window, slashed a roller blind with the machete and hurled their fire bombs, which had been made earlier at Bolland’s home, into the property.

One landed in the kitchen and another was hurled through an open doorway into the living room, landing between two settees and the doorway to the hall and stairs, ensuring the whole of the ground floor was engulfed in flames following two “ferocious” explosions.

Police believe Bolland, who had been inside the house before and knew the layout, deliberately wanted to aim the bottles, one of which had previously contained Budweiser and the other a wine or vodka bottle, so that there could be no escape.

The home was fitted with smoke alarms but investigators believe the intensity of heat from the explosions meant they melted before they were able to sound.

Upstairs the family was trapped, unable to get to safety down the stairs. Kyle and Bobby managed to climb out of a window and suffered smoke inhalation.

But Ms Pearson and the rest of the household were not so fortunate. Firefighters, who quickly arrived at the house, found Demi dead. Her younger siblings, Brandon and Lacie, were rushed to hospital but doctors were unable to save them.

Toddler Lia was alive but, after two days in hospital, doctors were unable to find any brain activity and devastated members of her family made the heart-breaking decision to turn off her life support machine.

The children’s mother, badly burned and severely injured, spent months in a coma, only regaining consciousness enough to be told of her children’s deaths two weeks before the murder trial was due to start.

She is likely to have to spend many more months in hospital but her family hopes she will be well enough to attend the children’s funeral later this summer.

Bolland had been involved in a series of disagreements with members of the Pearson family, threats had been made between them over a period of a couple of weeks and police were aware of an ongoing feud, so much so that security at the Jackson Street house had been upgraded, including fitting a device to prevent anything being pushed through the letter box.

“There were numerous minor squabbles over something extremely minor. They were very trivial fall-outs that rapidly escalated,” said DCI Lewis Hughes, from Greater Manchester Police, who led the murder investigation.

“I don’t think anyone could have foreseen Bolland would have come and done this.

“It rapidly escalated from a tit-for-tat feud to this.”

On the night of December 10, Bolland, Worrall, Brierley and others had been drinking, visiting shops to purchase alcohol.

Then, just before 1am Bolland and Worrall went to the Pearsons’ house and spoke to Ms Pearson, making threats against her family as she stood on the doorstep.

“Because of that visit they knew that the house was occupied,” said DCI Hughes.

The incident was reported to police by the Pearsons, who were looking for Bolland to arrest him, but before they could find him he had returned to the house with his petrol bombs.

The Pearson family did not ask to be moved from their home and DCI Hughes stressed that no one could have predicted they were in so much danger.

“I don’t think the family envisaged they were in this level of danger,” said DCI Hughes

During the murder investigation teams of officers trawled through hundreds of hours of CCTV footage from hundreds of cameras in the area in order to piece together Bolland, Worrall and Brierley’s movements on that night.

“It has been a massive process to be ready for trial,” said DCI Hughes.

At the petrol station Bolland and Worrall kept their faces hidden by pulling up hoods, but police were able to identify them by their clothing, the same clothing they were seen in on CCTV behind the Pearsons’ home, and the pair had to admit it was them at both locations.

Brierley was also at the petrol station, although out of sight of the CCTV cameras, and was in the getaway car on Alexandra Road, waiting for Bolland and Worrall.

Brierley tried to claim she was vulnerable and controlled by her boyfriend, Bolland.

But police found she was “integral in encouraging events,” including advising the other two about wearing gloves and keeping their hoods up to make identification difficult.

“She played a key role regardless (of not throwing a petrol bomb herself),” said DCI Hughes.

Throughout the investigation police took hundreds of witness accounts.

The jury was given a picture of Bolland, Brierley and Worrall of people who had previously involved themselves in a range of criminal offences and had not been averse to using violence.

But even after they were caught and had to admit they were involved in the fire bombing they sought to minimise what they had done.

Bolland made the unbelievable assertion that he thought the house was empty and Worrall, equally implausibly, claimed he thought they were at the house to commit a more minor offence.

However, a jury saw through their lies.

Because of the police’s previous involvement with the Pearson family, their handling of events leading up to the arson attack is now the subject of an investigation by the Independent Office for Police Conduct.