James Gargasoulas was a 26-year-old heavy drug user with an extensive criminal record when he drove a car at high speed through central Melbourne killing six people, including a baby boy and a 10-year-old girl.

He was sentenced to life in prison earlier this year for the January 2017 Bourke Street attack.

Despite a guilty verdict there are still outstanding questions about why Gargasoulas was able to carry out such a crime.

Much of the evidence against Gargasoulas has not been seen by the public before. In this painstaking investigation, months in the making, Four Corners reveals troubling failures to catch and hold Gargasoulas.

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