Union boss John Setka’s estranged wife threatened to kill him in “out of the blue” comments to a private investigator, a magistrate has found.

Magistrate Leon Fluxman on Friday found a threat to kill charge against Emma Walters proven.

She was captured in a recording telling private investigator Adrian Peeters: “I have to kill my children’s father to survive, you’re going to help me work out how I do it”.

The comments were revealed in a secret video played to Melbourne Magistrates Court, which Peeters said he was prompted to start recording by Walters also making the threat earlier.

“She out of the blue … uttered that she needed a piece,” Fluxman said on Friday.

The magistrate rejected Walters’ assertions that she was talking to Peeters as a friend, out of frustration and using “florid” language.

Rather, the pair had only spoken over the phone to organise a debugging job, she made it “absolutely plain that she had reached the end of her tether … and this was her last option”.

Her claim she was pushing the private investigator for a quote was “simply not credible”, the magistrate said.

Walters, 47, shared two children with the Construction, Forestry, Mining and Energy Union’s Victorian secretary.

The magistrate found Walters was at least reckless as to whether Peeters would fear she would carry out the threat.

She had faced an additional charge of attempting to commit an indictable offence, over police claims she tried to acquire a handgun.

But Mr Fluxman dismissed that charge, after Walters’ lawyer argued there was no evidence on the description of the gun.

Peeters said he began recording on his phone after about 10 minutes for his own safety, after she told him she wanted to “lure” Setka to the home.

“I know how to use a gun alright, and I’m willing to deal with the consequences of having to go through the court process of self-defence,” Walters is heard telling Peeters in the video.

“I have to kill my children’s father to survive, and that is not a very good position to be in.

“Anyway, you’re going to help me work out how I do it.”

She is then heard telling Mr Peeters she was a “lawyer by trade” and that “this conversation never happened … once it’s in the court you cannot say that you have any knowledge of it”.

Walters told police she didn’t want to kill John Setka but had to protect herself.

After leaving the property, Peeters said he contacted Setka, through the union, to warn him.

He then reported the incident to police.

– AAP