Abdullah AHH, 20, was arrested on Wednesday for the attack which saw Thomas L, 55, stabbed to death and another man, 53, seriously injured in Dresden on October 4.
The terrorist had only been released from prison five days earlier after he was jailed for two years and nine months in 2018 as an 18-year-old.
He arrived in Germany from Aleppo in 2015 as an unaccompanied minor and was granted refugee status in May 2016.
AHH lost this status because of his criminal record in 2019, but could not be deported due to the civil war in his home country.
Syrian ISIS supporter Abdullah AHH (pictured), 20, was arrested after a tourist was stabbed to death and another seriously injured in the eastern German city of Dresden on October 4
While living in asylum, the terrorist began recruiting for ISIS and threatened Christians, reported BILD.
Writing to a Christian, he said: ‘I will slaughter you today. You have a big mouth and I’ll cut off your tongue, you Christian.’
He was arrested in 2017 and categorised as likely to pose a threat to public safety, said Saxony state’s head of police, Petric Kleine.
Some 600 suspected Islamists are in this category in Germany, according to authorities.
In the 2018 trial, AHH was shown to have used ISIS symbols in his Facebook profile and also propagated jihad via social networks and called on like-minded people to fight as martyrs against so-called infidels.
A statement on the court’s judgment read: ‘The accused had been advocating a jihadist ideology since early summer 2017, increasingly turning to ISIS and finally, as its supporter, worried about carrying out an assassination attempt.’
AHH also searched the Internet for instructions on how to build an explosives belt, the court heard at the time.
He reportedly planned to bomb folk festivals including the Dresden bird meadow or the film nights on the banks of the Elbe in 2017.
The Syrian was released from prison, where he had served more than two years for recruiting members to a terrorist organisation, only days before the attack.
The victims of the attack in downtown Dresden were German men from the western state of North Rhine-Westphalia on vacation, according to the police.
A kitchen knife that investigators believe is linked to the attack was found at the scene with traces of DNA on it.
The victims, one aged 53 and the other 55, were German men from the western state of North Rhine-Westphalia on vacation in Dresden (pictured). The 55-year-old died later in hospital
In an assessment months before the attack, authorities had said it was highly likely the man would commit more crimes once released, Kleine said.
He was under observation on the day of the attack and the two preceding days, said the head of the Saxony branch of the domestic intelligence agency, Dirk-Martin Christian.
Mr Christian added that people just released from prison were not normally monitored 24 hours a day.
He said: ‘We are talking about an intelligence service that does not aim to avert danger, but to observe whether the person is moving in a radicalising environment.
‘The following could have happened. The observers sit in the car and watch the person. And suddenly he takes up his gun.
‘You’re in the car and, as bitter as it is, have to take note of it. Observation is not the appropriate tool to prevent such acts. It doesn’t matter whether we watch him for 24 or six hours.’
Abdullah AHH is charged with murder, attempted murder and dangerous physical harm for the Dresden attack.