Former Sydney teacher Chris Dawson was "very flirtatious" and "very vain" while interacting with a schoolgirl he would later marry, a close friend of the woman has told a court.
Mr Dawson has pleaded not guilty to murder in the NSW Supreme Court and denies involvement in the disappearance of his first wife, Lynette, 40 years ago.
The Crown case is that Mr Dawson allegedly killed his wife on or about January 8, 1982, in order to have an "unfettered relationship" with a student at the school where he worked, known as JC.
KL, a witness called by the Crown, today told the judge she had a circle of 10 friends at Cromer High, including JC, and Mr Dawson was one of her physical education teachers.
"What observations did you make of his interaction with [JC]?" Crown Prosecutor Craig Everson SC asked.
"He was very flirtatious, he was very vain," KL replied.
"[JC] was seen regularly standing in the door of his PE office, that's what I remember."
KL said she was "very close friends" with JC in year 11, who she described as "beautiful" but "very reserved".
KL told the court she received her high school results in January 1982 while on a camping trip to South West Rocks, on the NSW Mid North coast.
While sitting with JC, she saw Mr Dawson was standing behind them in the distance near his car.
"I said 'what is he doing here'," the witness said.
"We were all students."
According to KL, JC replied "I don't know" before her body language changed.
"She hunched up and sort of turned away from where he was."
JC's sister earlier told the court her home life in the early 80s was "pretty horrendous" due to "a lot of drinking" from her mother and step-father.
"We just stayed in our rooms and didn't come out," she said.
The woman told the court she was "taunted" at school by other students who would sing lyrics of the song Don't Stand So Close to Me, by the band The Police.
She said the lyrics were: "Young teacher, the subject of schoolgirl fantasy."
"It made me cringe," the sister said, explaining she "knew" they were referring to JC and Mr Dawson.
The sister also recalled the South West Rocks trip in January 1982 and said Mr Dawson was there at one point, but "did not stay overnight".
She was "fairly certain" she went home with JC and Mr Dawson, but could not remember the date they left.
Under cross-examination, the witness agreed other girls at her school had "crushes" on teachers and it was "not uncommon".
It was put to her that in a 1998 police interview, she said she used to cringe about the song, but would "secretly kind of smirk about it" because they were being "noticed".
"So deep down, there was something that made you feel good?" Mr Dawson's lawyer Greg Walsh asked.
"I wouldn't say good," the witness replied, before clarifying it was embarrassing.
The judge-alone trial, before Justice Ian Harrison, continues.
