A man accused of murdering three squatters by burning down an old Melbourne factory had allegedly threatened one of the victims, saying: "I'll burn you to your grave".

Darren Patrick Clover, 53, is charged with murdering David Griffiths, Tanya Burmeister and her 15-year-old daughter Zoe Burmeister by setting fire to the old ropeworks factory at Footscray on March 1, 2017.

Naomi Lane told a pre-trial hearing a man she knew as "Darren" threatened her friend Ms Burmeister  – Clover's ex-lover  – in the month before the fire, saying: "I'll burn you to your grave".

Ms Lane was with Ms Burmeister when "Darren" made the threat.

She said Tanya "shit herself".

"She just went quiet," Ms Lane told Melbourne Magistrates Court on Thursday.

"I was shaking. I went to walk after him and he just took off."

Ms Lane said it was the first and last time she saw "Darren".

Another witness, Ronald Thornton, said Clover asked him about a fortnight before the fire if he had seen Mr Griffiths, Ms Burmeister or Zoe, but he replied he hadn't.

"He was upset about it, he was thinking he was going to harm them or something," Mr Thornton told the court.

"He said he'd punch them up, get even with them and burn them.

"I never took him to be serious, but that's what he said."

Bich Thai, whose family home was near the factory, said about the time of the fire two males and a female were living inside and sometimes there were arguments.

She once overheard a fight between a woman and man, who was saying, "you don't love me anymore".

Clover has been charged with three counts each of murder and arson causing death, plus one count of damaging property by arson.

The committal hearing resumes on Friday.

AAP