A convicted killer slashed the friend of the man he murdered while serving his life sentence.
Anthony Allan struck James McGaughey in Glasgow's Barlinnie Prison.
The 29-year-old is on a minimum 18 year stretch for bludgeoning Ryan Richardson in Shettleston in March 2019.
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Allan fractured the sleeping dad's skull 17 times and was convicted of murder at the High Court in Glasgow.
It was four months later that he came across Mr McGaughey in the prison's exercise yard at 9am.
Prosecutor Alasdair Knox told Glasgow Sheriff Court: "Allan walked up to Mr McGaughey and had his arm around him as if to hug him.
"He had a large bit of glass in his hand and when we went to hug him he slashed him across the neck and cheek with it."
The men fought with each other before officers intervened and separated them.
Allan's cell was later searched and a piece of glass was found in cloth which he admitted was the weapon used in the attack on July 5, 2020.
Mr McGaughey was taken to hospital meantime for treatment to his cheek and neck.
A total of 27 stitches were used to close both wounds.
Mr Knox added that Mr McGaughey will be permanently scarred as a result.
Allan pled guilty to assaulting Mr McGaughey to his injury and permanent disfigurement.
Graeme Brown, defending, told the court that Allan believed that he was going to be attacked by Mr McGaughey.
The lawyer added: "He had received word that Mr McGaughey was the friend of his victim.
"He carried out this attack to prevent an attack on himself either then or at a later date."
Allan received no further time to his murder sentence after sheriff Brian Cameron imposed 21 months.
