Investigators have been left mystified by the case of a 70-year-old pensioner who burst into flames and died in front of horrified passers-by on a quiet London street.
Pedestrians watched in horror as they saw John Nolan ablaze in Orchard Place, north London, near Tottenham Hotspur's White Hart Lane football ground, just after 1pm.
Some desperately tried to put out the fire as others called the emergency services, the Daily Mail reports.
Mr Nolan, who was an unmarried, retired construction worker from County Mayo, Ireland, was flown to Broomfield Hospital in Chelmsford, Essex by air ambulance but died the next day. His body was 65 per cent covered in third-degree burns.
London Fire Brigade specialist investigators were unable to find anything at the scene that would have sparked a fire.
No property or any one else was harmed in the blaze.
Detectives are appealing for witnesses to come forward, to try to explain how Mr Nolan came to catch flames.
Met Police officer PC Damien Ait-Amer, the investigating officer on the case said: 'We have spoken with a number of witnesses who saw Mr Nolan abalze, but we have yet to establish how the fire started.
"Mr Nolan was a well-liked member of the community and none of our enquiries so far have indicated that he had been involved in a dispute of any sort.
"Nor does any account given by witnesses suggest that he had been in contact with another person at the time of the fire."
Mr Nolan followed his sister Mary to London in the 1960s and were later joined by their other three siblings.
He had been living in a few streets away from where he died in Tottenham.
A post-mortem examination gave his cause of death as severe burns. His inquest will open at Barnet Coroner's Court on March 13 next year.
No arrests were made in connection with his death, which happened on September 17 and it is still being treated as unexplained.
At the time, his family told the Irish Post of their heartbreak.
His brother-in-law Tom Byrne said: "John wouldn't hurt so much as a butterfly.
"In fact he'd find a way to bring the butterfly home and care for it. He was a gentle man who would do anything you asked of him."
He was described by neighbours as "gentleman" and a "truly lovely man".
Spontaneous human combustion: Terrifyingly unexplainable
Baffled investigators turn to spontaneous human combustion as the only logical explanation when people appear to burst into flames without any visible source of ignition.
There have been around 200 cases documented throughout history, with victims often elderly, sick, or under the influence of alcohol, which could explain why they are unable to escape the fire.
In November 2015 horrified onlookers saw a woman in her 40s burst into flames as she sat on a bench in Flensburg, north Germany.
Miraculously, she survived, but was rushed to hospital covered in burns.
The death of 76-year-old Michael Faherty in Galway, Ireland in December 2010 was the "first in 25 years" to be ruled the result of spontaneous combustion.
The coroner decided the fireplace in the sitting room where Mr Faherty's charred remains were found was not what caused his death.
Investigators were left bewildered when they failed to find anything that would have sparked the fire and no signs of foul play.
A 73-year-old man called Henry Thomas is believed to have spontaneously combusted at home in Ebbw Vale in 1980 in south Wales.
The fire left his entire body and half the chair he was sat in burnt.
Only his skull and a small part of his leg below the knee was left recognisable, incredibly with his trousers and socks still intact.
His glasses were found neatly folded in the grate of the fire and his slippers just beyond the remains of his feet - implying he had got comfortable in his chair before being set alight.
A woman called Mary Reeser was reduced to just her skull and part of her foot after her landlady knocked at her door to give her a telegram in St Petersburg, Florida in 1951.
Her remains were found among the ashes from a chair she had been sitting in, but there was little evidence of anything capable of starting a fire.
The first known account of spontaneous human combustion came from the Danish anatomist Thomas Bartholin in 1663.
He described how a woman in Paris "went up in ashes and smoke" while she was sleeping, yet the straw mattress she slept on was unharmed.
Puzzled scientists have come up with the "wick theory" to explain the mysterious phenomenon. The theory is that the human body can become an "inside out" candle.
The person's clothes are the wick, while their body fat is the wax or flammable substance, that keeps the blaze going.
Limbs may be left intact because of the temperature gradient, with the bottom half of the body being cooler than the top.
The combustion would not be "spontaneous" however, because it would need an external source to start it off, such as a cigarette.