Three men have been convicted of murder after deliberately starting a fire at a Leicester shop that killed five people, including a woman and her two sons, in a plot to claim a £300,000 insurance payout.

Arkan Ali, 38, Hawkar Hassan, 33, and Aram Kurd, 34, used dozens of litres of petrol in an arson attack on a Polish supermarket, triggering a huge explosion which tore through the shop and destroyed the flat above it.

They left Viktorija Ijevleva, a 22-year-old shopworker, to die in the building because she was aware of the insurance policy, which had been taken out less than three weeks earlier, Leicester crown court heard during the five-week trial.

Facebook Twitter Pinterest Left to right: Hawkar Hassan, Arkan Ali and Aram Kurd. Photograph: Leicestershire police/PA

Ali, Hassan and Kurd were unanimously found guilty of five counts of murder on Friday after they had denied murder and alternative counts of manslaughter.

They were also convicted of conspiring with Ijevleva, who was Ali’s girlfriend, to make a gain by dishonestly pursuing an insurance claim in respect of the fire.

Ijevleva, Mary Ragoobeer, 46, her teenage sons Shane and Sean, and 18-year-old Leah Beth Reek, who was Shane’s girlfriend, were all killed in the blast on 25 February in Hinckley Road.

Such was the ferocity of the explosion that some residents living nearby thought a bomb had had been detonated, the court heard. In fact, about 26 litres of petrol had been used to start the fire in the supermarket’s basement, causing the explosion just after 7pm.

CCTV and traffic camera footage released by the police after the trial show people fleeing from a nearby takeaway moments later. Rubble was also blasted into the road as cars passed.

Other footage police recovered from a neighbouring business showed Ali three days before the blast, moments before the angle of the camera was moved.

A day before the fire, other images from the same CCTV unit showed a gloved hand again moving the camera angle at a time when all the defendants were nearby. Another CCTV camera recorded Kurd escaping from the scene at the rear of the shop.

Facebook Twitter Pinterest Brothers Sean and Shane Rajoobeer with their mother Mary, three of the five victims of the explosion. Photograph: Leicestershire police/PA

Ali, Hassan and Kurd, who were remanded in custody, will be sentenced later this month.

David Herbert, prosecuting, told the jury at the start of the trial that the trio had intended to maximise the damage to the shop and would have been aware that people would have been in the two-storey flat above.

“The explosion and the proceeding fire demolished a building and killed five people in the building – one person who was in the shop and four who were in the flat above enjoying a peaceful night in,” he said.

“Even on camera 50 metres away you can see the explosion and the enormity of what happened. It was an explosion, the prosecution say, caused by many, many litres of petrol.

“The explosion and the fire that followed was deliberately caused by these defendants who intended to profit from loss of stock, contents and future loss of business from the shop. It was not an accident, the prosecution say, that the petrol used caused such devastating damage.”

Describing the unlawful killing of Ijevleva, Herbert said: “The defendants thought she knew too much and decided to leave her to die in the explosion that they created. In other words, the devastation that they caused was carried out with the intention to kill.”

Facebook Twitter Pinterest Viktorija Ijevleva was left to die because she was aware of the insurance policy, the court heard. Photograph: Leicestershire police/PA

A statement was read out on the court steps by DC Steve Markley on behalf of Jose Ragoobeer, the husband of Mary and father of Shane and Sean Ragoobeer. He said Mary was devoted to her family and had two jobs to ensure her sons had everything they needed. “She always made sure that the boys had the latest gear, including football kits for the teams they supported.”

Reek’s family said she had been looking forward to training as a nurse. Her older sister, Molly, said: “We have been asked to try to explain the impact on our lives after losing Leah in such horrific circumstances.

“She was an amazing, inspirational young lady who had only turned 18 last July. She was just starting out on her life adventure. In her 18 too short but wonderful years, she made a lasting impression on everyone lucky enough to know her.

“We miss her terribly, every second of every day we carry the pain of losing Leah. She has left a Leah-shaped hole in our hearts that nothing will ever fill. She was too special for anyone that didn’t know her to fully understand the impact her death has had on so many.”