The man who was charged in connection with an explosion at the Australian Christian Lobby offices in Canberra has committed suicide.

Jaden Duong, 36, had been accused of lighting gas cylinders inside a van parked outside the building, causing $10,000 worth of damage. 

He was expected to claim he was mentally unwell at the time.

His first committal hearing in court took place last month.

The ACL is among the groups that has been outspoken against gay marriage in the run up to the poll, warning that redefining marriage will threaten freedom of speech and take away religious freedom.

His defence lawyer, Peter Woodhouse, told the Canberra Times the man's death was further evidence that his alleged offence had 'always been a mental health issue and nothing more than that, despite what those opposite would like to assert'.

He said his client would probably have been found not guilty in the circumstances and urged others suffering mental health problems to reach out for help.

In an interview with police on the night of the explosion, after he had been treated in hospital for burns, Duong said he wasn't affiliated with any groups. He chose the ACL building because 'religions are failed'.

In a recent statement, police said they believed his main motive had been suicide: 'It is important for police to advise the public when an investigation into a terrorism incident has commence. It is just as important to advise the community where an incident is not believed to be terrorism-related.'