THE cause of a fire which killed three members of the same family will remain a mystery.

Lee Yates, 18, and sisters Joanne, 22, and Gail, 27, died in a blaze which engulfed the home of their mother, Rose, in Middlesbrough, last summer.

The sisters had moved to the house, in Pelham Street, after a fire at the house they shared in the town's Stowe Street.

After the first fire, Joanne was arrested on suspicion of arson with intent to endanger life, but there was insufficent evidence to proceed.

Gail told Cleveland Police she suspected Joanne, who had a history of self harm and a personality disorder.

An inquest yesterday heard that the three died from carbon monoxide poisoning and burns as fire swept through the Pelham Street house early on Saturday, August 23.

Detective Inspector Peter Jones told an inquest in Middlesbrough his investigation ed him to believe the fire was started by one of the victims.

"While the earlier fire in Stowe Street, coupled with her history or mental illness, appears to make Joanne Yates the most likely suspect, this can never be proved beyond reasonable doubt," he said.

"There will always be a remote possibility that the fire was started accidentally from a discarded cigarette."

He said it was unlikely someone had walked in off the street and started the fire, but it still had to remain a possibility.

"It may well be we will never know the true cause of the fire," said Det Insp Jones.

Occupational therapist Jane Harpin, working with the local mental health service, said arson was not a feature of Joanne's self harming.

Recording open verdicts on all three deaths, Teesside Coroner Michael Sheffield said: "The likelihood the fire in Pelham Street was started intentionally cannot be excluded, but cannot be proved beyond reasonable doubt. I have no alternative but to record an open verdict."

Gail's daughter, toddler Megan, survived the blaze but was badly burnt.

Last night, Rose Yates said: "You can see Gail in Megan. We have not had a chance to grieve properly yet because we have been concentrating on Megan.

"There was no other verdict they could come up with."