Yacqub Khayre, the 29-year-old gunman who killed a man, took a woman hostage and sparked a siege in Melbourne on Monday, was not on the radar of counter-terror police after his release from prison in December 2016, the ABC has learned.

Counter-terrorism investigators are now attempting to fill in the gaps about Khayre’s activities in the six months since his release from a Victorian prison over an aggravated burglary he committed while high on the drug ice in 2012.

Khayre, who was born in Somalia but spent some time in a Kenyan refugee camp before moving to Australia with his grandparents as a child, was well known to police and had an extensive criminal history.

His parents came to Australia in 2012 but a court heard his relationship with them was a difficult one.

In 2007 he was sentenced to two years in a youth justice centre for more than 40 charges of burglary, theft, assault and resisting arrest.

At the time of Monday’s attack he was living with his mother in Roxburgh Park in Melbourne’s north.

In 2009 Khayre was charged, along with four other men, with conspiring to do acts in preparation for or planning a terrorist act in relation to a plot to attack Holsworthy Army base in New South Wales.

He was alleged to have to travelled to Somalia in order to obtain a fatwa, or permission from a Muslim cleric, for the attack.

However, he and another man were acquitted.

The three others, Wissam Mahmoud Fattal, Saney Edow Aweys and Nayev el Sayed, were convicted and sentenced to 18 years each in prison.

In remarks after an unsuccessful appeal by the men convicted of the Holsworthy plot, the Victorian Court of Appeal noted that the defence in the original trial argued successfully that Khayre “regarded Australia favourably”, and that he did not have any apparent motive to plan a terrorist attack.

Khayre spent 16 months on remand in a high-security facility over the terrorism offences but was acquitted by a jury and released from custody two days before Christmas in 2010.

Read more: ABCnews