Killers will "literally be getting away with murder" if judges rule against a controversial law on so-called joint enterprise attacks, the widow of a former policeman who was stabbed to death has warned.
Tracey Fyfe, whose husband Paul was killed in 2011, spoke out ahead of a Supreme Court ruling on an appeal by one of the murderers, saying she would be "devastated" and "frightened" if he was freed.
Drug dealer Ameen Jogee was jailed for life alongside Mohammed Hirsi at Nottingham Crown Court in March 2012 after being convicted of Mr Fyfe's murder, even though he was outside the house when Hirsi stabbed the father-of-three.
Mrs Fyfe told BBC Radio 4's Today programme that she regarded Jogee as culpable for her husband's death because he knew what Hirsi was doing and was egging him on.
She said: "I think it is a very important law and it think it would be quite devastating for the victims' families like us, which would mean that criminals like Ameen Jogee would literally be getting away with murder.
"If Ameen Jogee hadn't been there that night neither would Hirsi. Ameen Jogee was using Hirsi as a weapon. Ameen Jogee intended to hurt somebody that night as he had picked up a knife earlier on and, in his words, he's threatened to 'shank' somebody.
"It's devastating. We have had four years of appeals, we can't move on, it just doesn't seem to stop."
A ruling on the principle of joint enterprise - which can result in someone being convicted of assault or murder even though they did not administer the blow - is scheduled to be published on Thursday.
A panel of five Supreme Court justices analysed the issue at a hearing in London in October when considering Jogee's appeal against his conviction for killing Mr Fyfe, who had been a detective with Leicestershire Police.
Jurors in the 2012 trial heard that Hirsi stabbed Mr Fyfe at a house in Leicester in June 2011 while being egged on by Jogee.
A judge imposed a minimum 22-year term on Hirsi, who lived in Leicester, and a minimum of 20 years on Jogee, who was of no fixed address, which was later cut to 18 years by the Court of Appeal.
Mrs Fyfe said she had no doubt of Jogee's guilt, saying he had appeared "angry and violent" when she had seen him in court.
She told Today: "(I'm) angry and disappointed, quite frightened, really, that he could be out on the street. He is a violent person and he'd be frightening to come face-to-face with really.
Novelist Ian McEwan aired the issue of joint enterprise in his 2014 book The Children Act, which centres on High Court judge Fiona Maye, who is asked to decide whether a 17-year-old Jehovah's Witness should have medical treatment against his wishes.
One of the characters, barrister Mark Berner QC, who is a friend of Mrs Justice Maye, has a client who was convicted of causing grievous bodily harm after becoming embroiled in a fight involving eight men.
''The prosecution pushed for joint enterprise,'' Berner tells Mrs Justice Maye in the novel. ''Same old story. My client played no part in that violence.''
A lawyer who specialises in criminal cases has said a review of law and practice relating to joint enterprise is ''long overdue''.
Sandra Paul, who works for law firm Kingsley Napley, said the Supreme Court ruling will have ''important consequences''.