The man who crashed a car full of gas cylinders in the Melbourne CBD before stabbing three people in a terror attack has been identified as Hassan Khalif Shire Ali.

If you or anyone you know needs help: Lifeline 13 11 14

Lifeline 13 11 14 GriefLine 1300 845 745

GriefLine 1300 845 745 BeyondBlue 1300 224 636

The 30-year-old was shot in the chest by a police officer and later died in hospital.

Here's what we know about the Bourke Street attacker.

Who was Shire Ali?

Hassan Khalif Shire Ali was born in 1988. He and his family moved from Somalia to Australia in the 1990s.

Police say his family is well known and respected within the Somali community in Melbourne.

They attended the Virgin Mary Mosque in Hoppers Crossing, west of Melbourne.

Shire Ali most commonly attended prayer in Melbourne's northern suburbs.

He was married. His wife is speaking to police.

Shire Ali had lived with family in Werribee but the ABC has been told he recently moved from the home because of problems with substance abuse.

Sorry, this video has expired Police and bystanders confront the knife-wielding Hassan Shire Ali.

What did police know about him?

Shire Ali was known to intelligence agencies and police.

His passport was cancelled in 2015 when the Australian Security Intelligence Organisation (ASIO) believed he planned to travel to Syria.

Police say he held radical views and had links to the Islamic State (IS) group.

However, Shire Ali was never targeted by a Joint Counter Terrorism Teams (JCTT) investigation because an assessment was made that he did not pose a threat to national security.

He was not actively monitored.

JCTT will now investigate how and when he moved from having those radical views to carrying out the attack.

Sorry, this video has expired AFP says Bourke St terror suspect was known to them

What was his motive?

Police say Shire Ali was radicalised and inspired by IS.

However, it is not yet known if there was direct contact between him and the group.

His attack has been declared an act of terrorism intended to cause maximum casualties.

Police are investigating why the attack was carried out on Bourke Street — an iconic precinct in the Melbourne CBD.

It is a popular area and was full of people when the attack happened on Friday evening just before peak hour.

Shire Ali's car was full of opened gas cylinders and caught fire after he crashed it. ( AAP: James Ross )

Did he have help planning the attack?

Police believe the threat of the attack was limited to Shire Ali.

His family members and associates are a key focus of the investigation.

Raids have been carried out on properties in the Melbourne suburbs of Meadow Heights and Werribee.

The set up of gas cylinders in Shire Ali's car, deliberately opened to cause an explosion, was described by police as "not remotely sophisticated".