Shahid Mohammed had become enraged when his sister, Shahida, had become involved in a relationship with a man named Saud Pervez.
Controlling Mohammed did not approve and aimed his rage at Mohammed Ateeq-Ur-Rehman, known as Ateeq, who had supported Shahida and Saud's relationship.
On May 12, 2002, Mohammed carried out the ultimate revenge on Ateeq and the Chishti family, who were asleep at their home in Osborne Road, Birkby, when Mohammed and another man, Shaied Iqbal, armed themselves with petrol bombs made from milk bottles which were thrown through the double-glazed lounge window.
They also poured petrol in through the letterbox and ignited it.
After getting back into the car, Iqbal was described as being "very happy and smiling", with Mohammed saying: "Did you see the way it went up?"
The flames quickly engulfed the house causing mass devastation.
Miss Aziz's brother, Ateeq, 18, also died in the fire, and their mother, Zaib-un-Nisa, 54, died a week later in hospital after jumping from a window to escape the flames.
During the five-week trial at Leeds Crown Court, one surviving member of the Chishti family, Siddiqah Aziz, told how she managed to save her father, Abdul Chisti, from the inferno but was prevented from coming to the aid of other family members when she was met by a wall of flames.
She said: "When I went downstairs, the smoke was coming through the front room. I got my dad through to the cellar, because he was really weak, and I came back for the others.
"But when I came back the fire was too strong, it was too much."
Mohammed was seen running away from the scene by witnesses and quickly became a main suspect of detectives at West Yorkshire Police.
He was investigated by officers at the time, but skipped bail and fled to Pakistan prior to a 2003 trial in which Iqbal was convicted of eight counts of murder, while Nazar Hussain and Shakiel Shazad were both found guilty of eight counts of manslaughter in relation to the fire.
He had been held in prison in Pakistan since he was located and arrested in Rawalpindi on 22 January 2015 following a joint operation between West Yorkshire Police, the NCA and Pakistani authorities.
During the trial Mohammed maintained he had only acted as a look-out, that he had been under the impression that the plan was to petrol bomb a car and that he did not intend to throw anything.
He showed no emotion as the jury found him guilty of eight counts of murder and one of conspiracy to commit arson with intent to endanger life.
The guilty verdict has been welcomed by West Yorkshire Police.
“This incident remains the biggest single event of multiple murders that West Yorkshire Police has investigated. It has been an extensive and protracted enquiry with a large team of detectives tirelessly working to secure justice for the family. At the end of last year, we were successfully able to extradite Mohammed from Pakistan with the assistance and support and several agencies both here in the UK and abroad.
“Since 2002, the Chishti family has shown nothing but dignity throughout this unimaginable tragedy for their family. I would like to express my greatest condolences and gratitude to them for all these years and I wholeheartedly welcome the verdict handed to Mohammed after he attempted to evade justice for so many years.”
West Yorkshire Fire and Rescue Service Area Manager, Chris Kirby, said: “This was a tragic incident which had a devastating impact on the family and the wider community, as well as being distressing for the firefighters and investigators who dealt with the aftermath.
“In this case the speed and ferocity of the fire gave little chance of escape due to accelerants being used. We condemn deliberate fire setting in any circumstances however the details of this case are particularly abhorrent.”
Mohammed will be sentenced at Leeds Crown Court tomorrow.