A 21-year-old gunman who killed nine students and a teacher at his former school in Austria had developed a fascination and "significant passion" for such shootings in recent years, investigators say.

Police say the former pupil planned last Tuesday's roughly seven-minute attack at the BORG Dreierschützengasse high school in Graz down to the smallest detail - but are still uncertain as to the motive for his rampage.

They have also flagged a series of copycat threats that are causing disruption.

After the shooter's body was discovered, investigators found he still had 24 bullets in two magazines and another 18 loose bullets for his Glock handgun, along with 17 bullets for his shotgun, according to Michael Lohnegger, the head of Styria province's criminal police office.

This has led to questions about why he decided to stop shooting when he did.

Detectives continue to trawl through a string of social media accounts attributed to the man - who has not been identified - to determine which are genuine.

They can "say with certainty that, over the years, he developed a significant passion in general terms for the phenomenon of school shootings," Mr Lohnegger said.

"He glorifies not just the acts in general, but also the perpetrators who carried out these acts."

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Eleven people were also wounded in the shootings last week, after which the gunman also died by suicide. Two of those wounded have so far been released from hospital. Two remain in intensive care.

Police also highlighted an ongoing issue with copycats making threats. In Graz alone, their threats have triggered around 30 police interventions in the past few days, the Styrian Police Department said.

Austria's Chancellor Christian Stocker said gun laws in the country, which are among the more liberal in the EU, will be tightened in the wake of the attack.