Austrian officials have confirmed the assailant believed to have carried out Monday's deadly terror attack in central Vienna was Kujtim Fejzulai, 20, a sympathizer with the so-called Islamic State (ISIL). 

Fejzulai, alleged to have killed four civilians – including a Chinese Austrian – and injured 14 more people on November 2, was heavily armed when police shot him dead just nine minutes after he launched the attack. 

However, questions remain over why the suspect, who was convicted of a terror offence only last year, was given early release from prison and how he managed to plan such a deadly attack under the nose of Austria's security services. 

And according to Austria's interior minister, Karl Nehammer, the answers could force the country to re-evaluate its justice system.

Conviction and release

Prior to Monday's attack, Fejzulai was sentenced to 22 months in prison in April 2019 for attempting to travel to Syria to join the extremist militant organization ISIL. 

However, the Austrian-born son of immigrants from North Macedonia was released on parole in December, leaving jail early because of his young age and his apparently successful completion of a deradicalization program.

Speaking during a press conference on Tuesday, Nehammer said: "The perpetrator managed to fool the justice system's deradicalization program, to fool the people in it and to get an early release through this." 

However, "despite all the outward signs that he was integrating into society, the assailant apparently did exactly the opposite."

Despite his conviction and being known to the Austrian security services, Fejzulai was able to go on to amass a small arsenal, including an automatic rifle, a hand-gun and a machete. 

He posted a photo with the weapons on his Instagram account before launching one of Vienna's first major terror attacks.

Read more: Vienna terror attack: Eyewitnesses, reaction and what we know so far

Under observation

Fejzulai's profile and the Austrian government's failure to pick up on his activities echoes similar extremist incidents in Europe where security services were too late in apprehending those planning attacks. 

Britain's security services, for example, were heavily criticized by a parliamentary watchdog for missing several chances to prevent the 2017 Manchester Arena attack carried out by bomber Salman Abedi, who was well known to the UK's MI5 intelligence agency.

When asked if Fejzulai had been under observation, the Austrian interior minister replied: "He really was so intelligent and so slick in deceiving those around him, we could not have expected anything like that." 

However, Vienna police chief Gerhard Puerstl said at the same conference that other people who have shown support for ISIL were under observation.

Despite having come to the conclusion that the 20-year-old had likely carried out the attack alone, police have already arrested 14 people linked to Monday's attack in 18 separate raids, including at Fejzulai's home.

Nehammer added: "We need to look very closely, especially among those who have been in contact with [Fejzulai].

"This is the basis of the investigations that are being carried out right now."

Read more: Terror-hit Austria starts virus curfew as lockdowns increase: COVID-19 daily bulletin

Fractures in the system

Monday's tragedy follows several militant attacks in France, including an assault on churchgoers in the Mediterranean city of Nice, with security experts warning about the danger posed by homegrown European extremists.

The recent republication of cartoons of the Prophet Mohammed in France have stirred new tensions, sparking protests in some Muslim-majority countries and calls from several militant groups for their followers to take vengeance. 

Following the Vienna attack, Britain has raised its terrorism threat level to "severe," meaning an attack is now seen as highly likely.

In Austria, the government is attempting to get on top of the attack as quickly as possible – and looking at how it can prevent similar situations from happening in the future, in a country where terror threats have been relatively low.

Asked whether the deradicalization program had failed in the case of Fejzulai, Nehammer said there had been a "fracture" in the system. 

He added: "Henceforth, we have to look at how ... you can find these people who want to destroy the democratic culture of freedom and stop them from carrying out the crime that they want to commit later."

He said that while he did not want to "point fingers ... we must look very closely at what can be improved."