Lachlan Young is accused of threatening Hannah McGuire two weeks before he allegedly murdered the 23-year-old and burnt her body in a ute in remote bushland.
Young admits he killed Ms McGuire on April 4, 2024, but has pleaded not guilty to murder, claiming her death was a spontaneous and unplanned incident.
Danielle McCann, the business manager of the Delacombe school where Ms McGuire worked, said the school was effectively locked down on March 20, 2024, because of Young's threats.
"(Hannah) came into my office and said she had been receiving threatening phone calls - he was threatening he would come to the school," Ms McCann told the Victorian Supreme Court on Tuesday.
"I notified the principal and other staff. We made sure all external doors to the building were locked."
Ms McGuire wanted to take her students into the yard like she usually did, so Ms McCann said she advised her to stay close to the office door.
Other staff members also kept an eye out for Young in case he came onto school grounds, Ms McCann said.
Ms McGuire had previously told Ms McCann she was seeking an intervention order against Young following their break-up earlier in March, the business manager said.
Ms McCann said she told the school leadership and office staff that if Young ever came to the school, they should say Ms McGuire was away on a professional development session.
"She didn't feel safe," Ms McCann said.
Some of Ms McGuire's other colleagues and friends also gave evidence on Tuesday about Young's alleged abusive and controlling behaviour.
Jaymie McDonald told the jury Young always appeared disrespectful to Ms McGuire and called her a "fat bitch" after he saw a photo of her eating a potato cake.
Young also came to every 'girls night' Ms McDonald and her friends organised with Ms McGuire, she said.
He also ordered Ms McGuire to come home and stop having fun when she went to Melbourne for Ms McDonald's birthday, the friend told the jury.
Ms McDonald said after Ms McGuire broke up with Young, she appeared happier and stronger.
"She had found such a glow," the friend said.
It's alleged Young murdered Ms McGuire a few weeks after she separated from him.
The trial before Justice James Elliott continues.
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