The march, led by President Heinz Fischer and other members of government, followed the route driver Alen R. took as he drove through the city at high speed, injuring 34 people.
12,000 people gathered for a memorial service in Graz's main square.
Graz Mayor Siegfried Nagl said that “words failed him” but that he was grieving for the victims - newly wed 28-year-old Adis, four-year-old Valentin, and a young woman who has still not been identified.
Chancellor Werner Faymann expressed condolences for the "families of the victims". "The suffering that this killing spree has caused them can never be undone. Solidarity means that we stand together in good times and in times of crisis…”
26-year-old Alen R. was arrested shortly after his killing spree and is still being questioned by police and examined by psychiatrists.
According to media reports there have been differing assessments of his mental health, with one expert saying that he is “play acting” and planned his attack with great precision. Other reports suggest he has severe mental illness.
More details are emerging about his family life, with neighbours telling the Kronen Zeitung tabloid that he would take pot shots with a rifle from his window, threatened neighbours and beat his wife.
He told police that he felt “persecuted” and felt compelled to kill.
He was born in Bosnia but fled with his family to Austria as a young boy to escape the war.
He and his parents set up a car dealership. Their neighbours say that they were responsible for a “reign of terror” and were abusive and antisocial, but that police ignored complaints.
Alen R. is married and has two children. He had to leave the family home and had a restraining order placed on him after being abusive to his wife. She said he wanted to force her to wear a headscarf and she had to seek refuge at a women's shelter after he beat her up.
Shortly before he went on his murderous rampage he destroyed his mobile phones and deleted content from his Facebook and Twitter accounts.