A man who allegedly held a female work colleague hostage and murdering her brother has been committed to stand trial in the Northern Territory Supreme Court.

Police allege that, in April last year, 36-year-old Matthew Vanko tied up and robbed Noelene Stevens at her Humpty Doo home and then stabbed her brother Donald Stevens, 53, in the back of the head.

The former Darwin detention centre security officer has been charged with six offences, including murder, deprivation of liberty and aggravated assault.

The Darwin Magistrates Court heard from a number of witnesses, including Ms Stevens and other ex-work colleagues of Vanko during a two-day committal hearing.

Some of Vanko's colleagues described him as "strange" and said that he made them feel uncomfortable.

Ms Stevens told the Darwin Magistrates Court she thought she was going to be killed.

She gave her evidence via a videolink.

She told the court that Vanko panicked when a helicopter flew over her property and that he pointed a gun at her.

Ms Stevens also told the court that she agreed with whatever Vanko said because she was "struggling to survive".

Vanko will appear in the Northern Territory Supreme Court in April.