A 20-year-old native of the city, who had previously been jailed for trying to join Islamic State in Syria, was shot dead by police within nine minutes of opening fire on bystanders and bars on Monday. He killed four people.
Fifteen arrests have been made since the attack, but Interior Minister Karl Nehammer conceded on Wednesday that "some things went wrong" in processing intelligence from neighboring Slovakia in July that the attacker had tried to buy ammunition.
Nehammer and Chancellor Sebastian Kurz have also said, however, that the attacker was released from prison too soon because he fooled a deradicalization program as to his rehabilitation. The organization running the program denies that.
"I am appalled. I don't know about surprised, but I am still very upset that it took you less than 24 hours for you, Mr. Chancellor and you, Mr. Interior Minister, to start blaming others in the justice system," the head of the liberal Neos Party, Beate Meinl-Reisinger, told parliament.
Nehammer and Kurz are both from the conservative People's Party (OVP).
The attacker was released early in December last year and his sentence would have run until July of this year.
In his speech to parliament Kurz pointed to the early release and said the attacker lived free and undetected "only because he falsely declared to turn his back on terror."
The organization that runs the program, Derad, has said that was not true, because the court ruling on his early release made no mention of deradicalization and his case officer never said he was radicalized.
In an interview on ORF TV on Wednesday evening Justice Minister Alma Zadic, from Kurz's junior coalition partner the Greens, did not go into specifics on the case but said the deradicalization program and those who are enrolled in it should be monitored more closely.
Interior Minister Nehammer has also accused his predecessor Herbert Kickl, of the far-right Freedom Party, of weakening the country's main intelligence agency, the Federal Office for the Protection of the Constitution and Counterterrorism (BVT).
The leader of the Social Democrats, Pamela Rendi-Wagner, said that while Kurz was calling for the country to unite, he was in fact doing the opposite."When will you understand that it is never the time, especially not now, to shift responsibility? That now, in this difficult moment, it is not the time to blame each other within the government?" she said.