Double murder investigation was underway after a talented golfer and his eight-year-old sister were killed in a house fire.
Thomas Sharkey, 21, and his younger sibling Bridget were killed in the blaze which police believe was started deliberately.
Their parents Angela, 46, and Tommy, 55, managed to escape the fire in Helensburgh, near Glasgow, after an off-duty policeman raised the alarm.
They were both being treated in hospital for serious injuries.
The tragic eight-year-old girl is believed to have died after coming home from a planned sleepover because she missed her parents.
The heat of the blaze caused a downstairs window to explode and left an area of severe scorching around the front door of the property in Scott Court.
Detective Chief Inspector Anne McKerchar, the officer in charge of the investigation, added: “This is a tragic event made worse by the fact that it was a deliberate act.”
She appealed for anyone with information to come forward as a “matter of urgency”. Police refused to name the victims until all next of kin were informed but confirmed a 21-year-old man had died.
They said a 55-year-old man, his wife, 46, and their eight-year-old daughter were taken by ambulance to the Royal Alexandra Hospital in Paisley, where the young girl died a short time later.
The man was later transferred to Glasgow Royal Infirmary but both parents were being treated for serious burns.
The tragedy happened while Thomas Sharkey was home from Georgia Southern University in Statesboro, Georgia, USA, where he was working on improving his golf.
A member of staff in a local supermarket, who did not want to be named, said: "It's absolutely tragic. The little girl was in here just last night. She was very talented and even drew us a card at Easter."
She said the family had recently returned from a trip to the US to see Thomas junior. He was a member of Helensburgh Golf Club, where he was a former junior and senior champion.
According to posts on Georgia Southern University's website, he described himself as "ambitious and competitive" and his main hobbies were golf and football.
Fraser Hall, a professional at Helensburgh Golf Club was too upset to discuss the tragedy yesterday. "Things are just too raw just now," he said.