Paul Smith, 47, told a court it was a "cowardly act" not to get help for Lynda Spence, 27, when she was being held at a flat in West Kilbride, Ayrshire.
Smith was previously charged with murder along with Colin Coats, Philip Wade and David Parker, 38, but he and Parker had their pleas of not guilty accepted by the Crown when they admitted assaulting her and attempting to defeat the ends of justice.
At the High Court in Glasgow yesterday, Smith was called as a witness in the prosecution's case against Coats and Wade.
He said his understanding was that the woman was in danger because she had people looking for her, but when Ms Spence was brought to Parker's flat in Meadowfoot Road on April 14, 2011 it was a different situation completely.
Smith said Ms Spence was bound to a chair by her arms and waist with silver tape, with her feet taped together and she had dark sunglasses on which were taped inside.
During the first few days of her being held in the attic of the flat, Ms Spence told the witness that Coats had cut off the tip of her pinkie finger and crushed her little toe with loppers, which Wade had brought with him in a bag, jurors heard.
He told the court: "It was a cowardly act not to phone the police, on my behalf. The fear factor had set in with what was going on. We were involved in it, we were in the fold.
"I thought it was easier just to do what Mr Coats said, and not argue with him. I quite liked my fingers the way they were."
The trial continues.