Vienna: Austria is investigating 21 people as possible accomplices of the jihadist who went on a deadly shooting rampage in Vienna last week, but much remains unknown, including how he got to the area of the attack, officials said on Friday.

The 20-year-old Vienna native armed with an assault rifle, handgun and machete killed four people in a part of the city centre with many bars that also houses Vienna’s main synagogue, which was closed at the time. He was shot dead by police.

“No one else was immediately involved in carrying out this crime on Nov. 2. What we cannot yet say definitively is to what extent accomplices provided support before the act,” the police official leading the investigation, Michael Lohnegger, told a news conference.

Vienna prosecutors’ office spokeswoman Nina Bussek said the number of people remanded in custody over the attack was unchanged at 10, and 21 people in total were under investigation, aged 16-28. As yet unknown additional accomplices are still being looked for.

Austria has admitted to an intelligence failure before the attack since it mishandled information that the attacker tried to buy ammunition in Slovakia in July, and that he met known foreign Islamists that month - two from Germany who were under surveillance and two from Switzerland who have been arrested.

It remains unclear how the attacker carrying weapons, ammunition and a dummy explosives belt travelled to the city centre more than 10 days ago.

“What we can currently actually rule out here is that the perpetrator arrived at the crime scene by public transport,” Lohnegger said, adding that other forms of transport including taxis were still being worked on.

“Whether it is also possible that he walked to the scene of the crime, I cannot say. That means I also cannot rule it out.”