A scientist told a murder trial yesterday she believes the fire which led to teenager Jessica McCagh’s death was caused by a naked flame.
Fire investigations specialist Rebecca Peplar said the suggestion that debris from a cannabis joint smoked by Miss McCagh’s boyfriend had ignited the blaze was “so unlikely that it can be dismissed”.
She also said at least a litre of petrol was involved in the fire and she found Miss McCagh’s burnt clothes had an extremely high level of the fuel on them.
Her evidence came as jurors watched a film of a series of experiments which showed that the only thing able to ignite petrol vapour was a flame from a cigarette lighter.
Ms Peplar was giving evidence at the High Court in Livingston on the seventh day of the trial of Miss McCagh’s boyfriend, 18-year-old Stewart Blackburn. He admits killing 17-year-old Miss McCagh at his home in Bloomfield Road, Arbroath, but denies murdering her.
Prosecutors allege Blackburn doused Miss McCagh in petrol and set her on fire. The trial heard previously that Blackburn confessed in a police interview to “slapping” a jerry can of petrol at Miss McCagh during a row.
He said after the argument he lit a joint which ignited the blaze on April 25.
Ms Peplar, 34, a manager of forensic services at a company near Reading, told the court yesterday she carried out a series of experiments on igniting petrol vapour.
In the film of her tests shown to the court, she is seen trying to ignite splashes of petrol and a tray of petrol in various ways.
The only thing which set the petrol on fire was a naked flame from cigarette lighter held about a centimetre away, the court was told.
Ms Peplar told the court that the ignition of petrol vapour by debris from Mr Blackburn’s cannabis joint was “so unlikely that it can be dismissed”.
“It is my opinion that the fire was caused by a naked flame,” she told the court.
Asked about the amount of petrol she believed was on Miss McCagh and at the scene of the fire, she replied: “I would say at least a litre. I would probably say it’s more than that but I wouldn’t like to quantify.”
She told the court there have been “no reported scientific experiments where petrol has been ignited by a lit cigarette”.
Ms Peplar said her investigations at Blackburn’s flat revealed that the bedroom door had been “closed for the majority of the flaming fire”.
She also found that the handle on the door had signs of mechanical damage, which she said was due to force.
The witness said it was “entirely consistent” with the suggestion that the bedroom door had been held shut.
Describing the blaze as “rapidly developing”, she said: “The amount of heat produced would have been considerable.”
Earlier, Ms Peplar said scientific tests on Miss McCagh’s burnt clothes showed a higher level of petrol within them than that found on the inside of a petrol can. The witness said she could not recall having seen another piece of burnt clothing which came up with such a high reading.
She went on to say the reading was “higher, in fact” than that found inside petrol cans.
The trial, before Lord Bracadale, continues today.