A mother and her two sons were among the deceased in the explosion which destroyed the supermarket on Hinckley Road, Leicester.
Arkan Ali, 33, Hawkar Hassan, 33, and Aram Kurd, 34, caused the blast when they lit “many, many litres of petrol” in the basement of the Polish store.
All three defendants denied five counts of murder and conspiracy to commit fraud.
Mary Ragoobar, 46, and sons Sean Ragoobeer, 17, and Shane, 18, lived in the flat above the store and were at home during the “devastating” fire explosion on Sunday 25 February.
Shop worker Viktorija Ijevleva, 22, and Shane’s girlfriend Leah Beth Reek, 18, were also killed.
During the trial, jurors heard how Scotty Ragoobeer, who was 15 at the time of the incident, survived because he was dug out of the rubble by Leicestershire police and members of the public moments before the building was consumed by flames.
Prosecutor David Herbert QC told jurors the defendants purposely caused the fire, intending “to profit from loss of stock, contents and future loss of business from the shop.”
A five-week trial heard the defendants left Ms Ijevleva to die because she was had knowledge of an insurance policy taken out less than three weeks before the fire.
Mr Herbert said the three men “thought she knew too much and decided to leave her to die in the explosion that they created”.
Jurors, who took merely 11 hours to find the defendants guilty on all counts, were shown CCTV footage of people escaping from a nearby takeaway moments after the blast.
In the video, released by police after the trial, rubble can be seen flying into the road as cars pass by.
Further footage recovered from a neighbouring business’s camera showed Ali in shot three days before the blast – moments before the camera angle was changed.
Images taken from the same CCTV camera a day before the explosion showed a gloved hand moving the camera again – at a time when all three defendants were near the vicinity.
Kurd was also recorded on a security camera as he escaped from the scene from a rear exit of the shop.
Ali from Oldham, Hassan from Coventry and Kurd from Leicester will be sentenced on Thursday 18 January.
They were also found guilty of conspiring with Ms Ijevleva to dishonestly obtain an insurance claim after the fire.