A Russian woman who stayed at the same church as Angelika Kluk has told jurors she owed it to the murdered Polish student to ensure justice was done.
Rebecca Dordi was giving evidence for the defence
The trial at Edinburgh High Court also heard from a Catholic church press officer who questioned whether Angelika had been working as an escort girl.
Both testimonies were given on the first day of evidence for the defence.
Peter Tobin, 60, denies raping and murdering Angelika Kluk, and hiding her body between 24 and 29 September 2006.
Russian student Rebecca Dordi, 30, told the court that on the night that Angelika's body was discovered under the floor of St Patrick's Church in Anderston, Father Gerry Nugent appeared to know where the body was hidden.
Defence agent Donald Findlay QC asked Miss Dordi: "Are you able to say that on Friday night, Father Nugent knew where the body was?"
Miss Dordi replied: "He certainly did."
Mr Findlay asked: "Now you are a person who takes religion seriously and you have sworn by almighty God. Do you take this seriously?"
The witness replied: "Very, very seriously. I owe Angelika to help justice is done."
Miss Dordi also described how Angelika was being "flirty" with the man accused of raping and murdering her.
The witness said that she saw the Polish student and Peter Tobin in the garage at St Patrick's Church in Anderston the night before she disappeared.
During her testimony the witness said the pair were "laughing" and "giggling".
Ms Dordi said she went into the kitchen of the chapel house and was sitting reading when the two came in to make some tea.
Mr Findlay asked about the atmosphere, which Miss Dordi described as "over-friendly".
She added: "It looked as if Angelika was being flirty - not flirting but being flirty. There is a difference."
The witness admitted that she did not dislike Ms Kluk but did not approve of some of the things she did.
She said: "We are different people. I certainly didn't approve of some of the things that were happening. I didn't approve of going round with hardly anything on, just a red robe.
Earlier the trial also heard about the behaviour of Father Nugent, the day after Ms Kluk was reported missing.
Catholic church press officer Simon Dames, 34, described how he was summoned to St Patrick's by an urgent phone call and during a conversation with the priest wondered if Ms Kluk was an escort girl.
Mr Dames described the phone call from the priest as "anxious" adding "maybe tipping towards nervous".
However, the witness said that when he got to St Patrick's chapel house on Tuesday 26 September the priest had changed.
"He was calm," Mr Dames told Mr Findlay
Mr Tobin denies murder, attempting to defeat the ends of justice, and attempting to pervert the course of justice.
He also denies rape, claiming he had sex with Angelika with her consent.
The trial continues.