Ian Clyde, told the High Court in Glasgow that David Parker and Paul Smith were at his house in April 2011 and told him they were "babysitting" a woman.
Mr Clyde's then girlfriend, Laura Main, told the court she has ended up in a psychiatric unit after what had been said.
Colin Coats, 42, David Parker, 38, Paul Smith, 47, and Philip Wade, 42, deny abducting, tortur-ing and murdering Lynda Spence at a flat at Meadowfoot Road, West Kilbride, in April, 2011.
Mr Clyde, 24, told the court Parker and Smith came to his house on April 17, 2011 and had a drink with him and Miss Main.
Solicitor General Lesley Thomson QC took the witness to a police statement he gave in January 2012.
In it he claims: "Paul Smith said 'Her scalp has already been done and they have cut her finger off'."
Mr Clyde – who was jailed the following day for an unrelated matter – told the court he did not remember it being said but accepted it was in his police statement.
Miss Main told the court she asked why they didn't let the woman out but was told that they couldn't.
The trial before judge Lord Pentland continues.