Police are being investigated over allegations around the death of murdered primary teacher Marelle Sturrock.
The force is now being probed by watchdogs over its handling of the murder-suicide in Glasgow.
The Sunday Mail understands the force is being investigated over claims around the time of the death of the mum-to-be.
Officials from the Police Investigations and Review Commissioner (PIRC) are now probing whether Marelle's life could have been saved before she was killed.
Marelle, 35, and her unborn child were killed by Yates at their home in Jura Street in the south west of Glasgow before he took his own life in Mugdock Country Park. His body was discovered in a reservoir on Thursday April 27.
Police Scotland said they could not comment on the PIRC investigation.
One source close to the investigation told the Sunday Mail the PIRC probe will look into "any failure in practice that could have saved Marelle's life of the lives of others in future."
A discretionary fatal Accident Inquiry could be held if the Lord Advocate believes there has been failures which could have prevented Marelle's death.
Officers believe Marelle’s murder could have been pre-meditated after claims that Yates took the couple’s beloved dog Sam to his mum’s house in Bearsden the night before the attack.
A source said: “It is thought to have been pre-planned because David brought the dog to his mum’s house the night before and told her he had plans the next day.
“It is not being considered as an accident - it was a brutal, frenzied attack.”
Marelle, a primary school teacher from Wick, moved to Glasgow at the age of 17 with the dream of working in the performing arts.
After studying musical theatre at Stow College she joined various local theatre companies where she met Yates, who shared her passion for performance, in 2011.
On her website, Marelle described how she developed a love of teaching from the people she met doing these stage performances and decided to go into the profession full time, first studying for her PDGE at Dundee University before getting a job at Sandwood primary school in Glasgow.
Family members, friends and colleagues have described her as a beautiful, talented, caring woman who loved children and who was excited about the prospect of becoming a mum.
One close friend said: “She was really excited about having the baby and she was brilliant with kids. All of this is a complete shock for us and for her family.”
Yates, 36, was one of four children and the son of renowned gynaecologist Robin Yates who died of cancer in May last year.
His sister is a professional photographer, one of his brothers a qualified pilot and the other a former professional international golfer.
A friend of Yates said he had struggled with his mental health in the past.
He said: “David had a bit of a breakdown before his dad died last year. He was in a band for a few years and wanted to make a go of that and he was still doing his theatre shows and things. Nobody can get their heads around what has happened here.”
Yesterday floral tributes and stuffed toys were left at the couple’s home while forensic officers worked outside.
A police cordon remained in place with officers guarding the scene.
Neighbours said police had carried out door to door enquiries following the death and had removed CCTV from outside a home nearby.
One said: “The house next door has CCTV which covers the front of the couple’s house and some of the back and the police have been in to take that.”
Another neighbour, who asked to remain anonymous, said: “I’d often see them in the garden and they would chat away as neighbours do.
“He would sometimes be outside with the dog and was a bit of a hippy, always playing the guitar.
“They seemed to have lots of friends and would sometimes have parties. But they kept themselves to themselves.
“Everyone is just so shocked, it’s just so sad.
“My wife saw a group of women last night who she said were teachers from the school where Marelle had worked.
“She was very well-liked, all the kids at the school loved her.”
Another neighbour added: ‘It’s just terribly sad. Whatever has happened, it’s just unthinkable.”
A Police Scotland spokesman said: “As this is being investigated by the Police Investigations and Review Commissioner (PIRC) we are unable to comment further.”
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