Police in Austria were hunting for clues on Wednesday after a gunman opened fire at his former high school a day earlier, killing nine students and a teacher in a deadly spree that stunned the country.

Austria to observe three days of mourning after a 21-year-old attacker kills at least 10 people at a school in Graz.

Police identified the suspected shooter as a 21-year-old from Graz, adding that he appeared to have died by suicide.