Initial reports suggested Mr Ali died after being severely beaten by the thief but a post- mortem examination yesterday showed bruises on his body were inconsistent with that.
But the police said they were still treating his death as murder and appealing for witnesses. 'In the pathologist's opinion, the heart attack was brought on by the emotional and physical stress of chasing and confronting the thief. Mr Ali did have a recent history of heart disease,' a spokeswoman said.
Mr Ali, 59, chased a man he saw break into his son Zaigham's car, parked outside the family home in Hornsey on Monday evening. He confronted the thief in an alley beside the house.
When his wife and daughter followed they found him unconscious on the ground. Passers-by and an ambulance crew tried in vain to resuscitate him, neighbours said.
Mr Ali's daughter, Farah saw the thief standing in a crowd at the end of the alley and shouted for people to grab him, but he escaped.
Friends and neighbours were quick to praise the popular businessman who owned tobacconist's shops at Bond Street tube station and Oxford Circus in central London.
John Dennis, a family friend and former employee, described him as a religious man, devoted to his wife and doting on his seven grandchildren.
'He was in semi-retirement but Mr Ali was the type of man who could never retire. He had to be busy, he had to be doing something,' he said.
The victim and his wife, Zamurd Ali, were due to be joined by their family to celebrate their 30th wedding anniversary yesterday.
His widow was being comforted by her eight-months pregnant daughter Farah, 27, and sons Zaigham, 29, and Zoeb, 25. Other members of the family were flying to join them from Pakistan.
'Mrs Ali and Farah are distraught. Her sons are in shock,' Mr Dennis said after visiting the family. 'It's not really sunk in. It still seems they have got a lot more to go through.'
He said cars were regularly broken into in the area. 'It gets to the stage where if any of us park our cars here we just don't leave anything visible. People round here will break into cars just for a jumper.'
Police described the man they want to question as black, 18-20, 5ft 9in, and wearing white training shoes, baggy turned-up blue denim jeans, a dark bomber jacket and a blue bandana with white stitching.