Steven Kavanagh, 41, told the High Court in Edinburgh that he saw David Gilroy, 49, arguing with Suzanne, 38, in the divorcee’s apartment at Crieff Hydro in October 2009.
The company director told prosecution lawyer Alex Prentice QC yesterday that the alleged confrontation took place as he was using the bathroom in Suzanne’s room.
He said that after leaving the toilet, Mr Gilroy asked him what he was doing in Suzanne’s room.
He said: “There were raised voices. The gist of it was that he thought I was intending to sleep with Suzanne. He was clearly unhappy. He was upset, angry.”
The development came on the eighth day of the trial of Mr Gilroy, of Silverknowes, who denies murdering Suzanne at Thistle Street, Edinburgh, or at another location in Scotland on May 4, 2010.
He also denies four other charges which allege he committed a series of criminal acts across Scotland between August 2009 and June 2010.
Mr Kavanagh said he came into contact with Suzanne Pilley on October 9 whilst they both attended a corporate function at Crieff Hydro.
He said that he had a number of conversations with Suzanne on the night in question whilst the pair had cigarette breaks.
Suzanne had told him that she had been in a relationship with David Gilroy but had broken up with him some time before the evening in question.
The court also heard that 24 hours after Suzanne Pilley went missing, Gilroy visited a school in Lochgilphead, Argyll.
The court heard that Gilroy’s employer IML was involved in the construction of the building.
Pc Alexander Grant, 33, said he was assigned by bosses at Lothian and Borders Police to the investigation that aimed to trace Ms Pilley.
Pc Grant said he had gone to IML in Thistle Street and spoke to colleagues of Suzanne who told him she had been in a relationship with David Gilroy.
Workmates also gave Pc Grant Mr Gilroy’s mobile phone number and the police officer spoke to Suzanne’s former partner after 5pm.
Pc Grant said Mr Gilroy told him he was in Lochgilphead. He also said he had last seen Ms Pilley on Monday, May 3 when he agreed to end their relationship.
The police officer told advocate depute Alex Prentice QC that he wanted to interview Mr Gilroy as soon as he returned to Edinburgh. This was because Mr Gilroy was a “significant witness” – officers believed at that point he was the last person to have seen Suzanne alive.
Mr Gilroy then allegedly said it would take him around four and a half hours to return to the Capital from Lochgilphead.
He then showed up at Corstorphine police station at 11.40pm and proceeded to be interviewed by police at five past midnight.
Pc Grant said he was present at the interview until 6am. The statement given by Mr Gilroy ran to 59 pages.
Pc Grant told the court that he felt Mr Gilroy wanted to co-operate with the police.
He added: “He was calm and he seemed fine. He was co-operative.”
The trial before Lord Bracadale continues.