THE identity of a second man who was seen with accused murderer Gordon Wood on the night his girlfriend was allegedly thrown to her death might remain a mystery, a Supreme Court jury has heard.

However, it does not affect the fact Wood was "legally responsible" for the model Caroline Byrne's murder, the Crown prosecutor Mark Tedeschi, QC, said in his opening address to the jury.

Wood, 45, a former chauffeur to the late stockbroker Rene Rivkin, has pleaded not guilty to murdering Byrne, 24, who was allegedly thrown from The Gap at Watsons Bay on June 7, 1995.

Mr Tedeschi said three witnesses saw a second man with Wood and Byrne at The Gap in the hours before her death. One witness, John Doherty, saw a second man standing by as Wood and Byrne argued near The Gap at 8 o'clock on the night Byrne died. About 11.30pm Mr Doherty and two fishermen heard a woman's terrified scream in the vicinity of where Byrne's body was later found.

Mr Tedeschi said that even if that second man had a role in the murder, "it was in combination with the accused". He said that Wood had the motive to murder Byrne as she was wanting to end their relationship and Wood did not want Byrne revealing information implicating Wood and his boss, Rivkin, in insider trading allegations.

The court also heard that Wood threatened a restaurant owner not to tell anyone he had seen him on the day Byrne was murdered. Mr Tedeschi said that Michael Jaggard, the owner of Alife restaurant in East Sydney, will testify that Wood dropped Rivkin at the restaurant at 1pm and returned about 3pm, in company with another Rivkin associate, Gary Redding.

Mr Jaggard will testify Wood spoke to Rivkin, who looked very agitated after the conversation. A few months later Wood threatened Mr Jaggard and on two other occasions told him not to tell anyone he had seen him on that day. He subsequently offered Mr Jaggard a lucrative share deal in the United Kingdom if he did not tell anyone, Mr Tedeschi said.

The jury heard that despite being on 24-hour call for Rivkin, Wood's mobile phone was off in the 11 hours before Byrne's death and was turned on only four minutes after her body was found, when he called friends and relatives. Mr Tedeschi said that despite telling her family he was anxious because Byrne was missing, Wood made no calls to her mobile phone the night she died, nor did he check his answering machine at their shared home in case she had called.

The jury inspected The Gap yesterday afternoon. Tony Byrne, Caroline's father, will give evidence today.