A woman has been found guilty of slashing child killer Theresa Riggi with a razor in ­Scotland's only all-women jail.

Angela Hamilton snuck into Riggi's cell at Cornton Vale Prison, Stirling, after breakfast and cut her face with a razor blade.

She left Riggi lying in her cell with her face covered in blood and a clump of her hair missing.

Hamilton then calmly walked back to her cell as prison guards rushed to Riggi's aid - alerted by her screaming.

Hamilton, 40, of Cambuslang, denied the attack but a jury of 10 women and five men at Stirling Sheriff Court took little more than an hour to find her guilty by majority.

Her lawyer, Murray Aitken, said Hamilton suffered from a variety of problems including drug abuse.

Sheriff William Gilchrist deferred sentence until October 3 for background reports, and released Hamilton on bail.

The incident occurred on November 19, 2011, while Hamilton was serving a six-year sentence for attempting to pervert the course of justice.

Riggi was in Cornton Vale during her first year of a 16-year sentence imposed for killing her three young children in Edinburgh. She has since died.

The court heard she was regarded as "a high-profile" prisoner.

During the two-day trial, prison officer Calum Graham told how he went to Riggi's cell that morning after hearing screaming, and saw Hamilton leaving the cell and Riggi lying on the floor inside with blood on her face, still screaming.

His colleague James McCabe said his hands and clothing became "covered in Riggi's blood" as he tried to help her.

Riggi, originally from California, USA, had a history of self-harm and had been diagnosed with a personality disorder and paranoia. She tried to kill herself twice in prison a week after being assaulted by Hamilton.

Jurors heard Riggi was found with a "ligature round her neck walking towards a set of stairs" on November 26, 2011, before being saved by prison staff. Later that same day she was found "drowsy and incoherent" in her cell and she said she had taken "40 pills".

She had previously tried to kill herself after fatally stabbing each of her children - eight-year-old twins Austin and Gianluca, and their sister Cecilia, five - at their home in the Scottish capital in 2010. She leapt out of the second-flood flat after trying to cover up their deaths with a gas explosion.

Riggi was originally charged with murder but admitted culpable homicide on the grounds of diminished responsibility.

The following year she was transferred to a secure mental hospital in England and was found dead there in March this year. A coroner ruled the 50-year-old died from natural causes - bronchial pneumonia - at Rampton Secure Hospital in Nottinghamshire.

Defence lawyer Mr Aitken said: "It seems a reasonable inference that at that time she was desperate to harm herself or kill herself in any way possible. It is not more likely that she inflicted these injuries herself?" He said that Hamilton, of Cambuslang, could have walked in on Riggi harming herself and screamed.

However, fiscal depute Claire Bremner told the jury: "There has been no evidence in this case that Theresa Riggi ever inflicted an injury on herself by cutting herself with a blade."

Hamilton was jailed for six years in 2009 when her brother walked free from a murder charge after she failed to give evidence at his trial. Following her failure to appear, her brother Daniel Hamilton was acquitted of murdering Paul White, 22, at a flat Pollokshaws, Glasgow in August 2004.

Her father Joseph Hamilton was found guilty of the murder and jailed for 17 years.