Mother Julia Trinne says she was 'ignored' by police while her husband murdered their son.

A bereaved mother who claims South Australia police refused to help her search for her missing son because it was outside of the station’s operating hours has lodged a formal complaint against the force.

Speaking to The AdvertiserJulia Trinne says she arrived at Norwood police station at approximately 7.30am on 8 July 2014, just 30 minutes after realising her four-year-old son Luca and mentally unwell husband David Janzow were missing. Seeing officers inside the station, Trinne knocked frantically on the station door, with police refusing to speak to her until the station officially opened at 8am.

Luca Janzow. Source: Facebook / David Janzow.

“I could see people in the station but they would not open the doors because it was not opening time,” Trinne said, continuing, “I understand protocols but when it is obvious something major is wrong you would think surely they would be able to realise this and act.”

At the same time, Janzow, who had a long history of mental health issues and had been diagnosed with depression and bipolar disorder, was murdering her son.

Luca Janzow. Source: Facebook / David Janzow.

When Trinne was admitted into the station, she says police were more focussed on the fact that she could not remember her husband's car registration than anything else.

Following his arrest, Janzow told police he had killed his son because he was a psychopath and believed his son showed signs of the same behaviour. The murder, he said, was an attempt to "save Luca from what was to come."

Janzow was ultimately found not guilty of murder due to mental incompetence.

Video by 9 News Adelaide

Trinne, who now lives interstate, has said she plans to demand a coronial inquest into Luca’s death.

South Australia Police refused to comment on Trinne's complaint and the investigation that is currently underway into the police's response.

If you or someone you know needs help you can contact Lifeline on 13 11 14.], the Kid's Helpline on 1800 55 1800 or the Men's Helpline on 1300 78 99 78.