Serco worker kidnapped boss: lawyer

A former Serco immigration detention centre employee had reached a crisis point at work when he took his supervisor hostage and killed her brother and his dogs, the Darwin Supreme Court has heard.

Matej Hoi Stung Vanko, 37, has pleaded not guilty to depriving Noelene Stevens of her liberty, and to murdering her brother Donald on April 23, 2012.

Things came to a head at work on March 14, 2012, Crown prosecutor David Morters said on Friday.

"Your conflict with work colleagues and managers was coming to a crisis point ... Noelene Stevens preventing you taking up positions you thought you were entitled to ... was the root of all your problems at Serco," he alleged.

Vanko denied this.

He had a female friend drive him to the Stevens' property while he hid in the backseat, the court heard.

"It was not an innocent visit," Mr Morters said.

Vanko admitted on Thursday to casing the house "to see Don lived where he said he lived".

Donald Stevens lived with his sister Noelene.

Vanko told the court he didn't kill Mr Stevens because he spent all day with his friend Bridget Tomlin in Palmerston, outside of Darwin, from 11am until about 9pm.

But despite saying he had visited her at home on four occasions, he could not recognise her house in photos, did not remember where he parked, whether they sat in the lounge or the bedroom, whether other people were in the house or whether he spoke to them.

He did not have her phone number saved in his mobile and telephone records showed he had never called her, the court heard.

Mr Morters said that in fact Vanko had never met her until September 6 last year, 10 days before his trial was due to begin.

He was kept in the same prison accommodation area as Ms Tomlin's brother for extended periods, Mr Morters said.

"He is such a good friend that he organised for his sister Bridget to meet with you ... you met her so you could organise with her to provide an alibi for you," he said.

"(She) didn't even know your name before that meeting."

"I disagree with that," Vanko replied.

The trial continues.