Authorities in Austria were trying to find out why a 21-year-old shooter targeted his former high school, killing 10 people before taking his own life. This incident marked one of the most violent attacks in the nation’s recent history.

Police said the man, armed with a shotgun and a pistol, acted alone.

The officials are examining the gunman’s residence and online activities to understand his motives for carrying out the shooting at the school in Graz, the second largest city in Austria, on Tuesday. Shortly after the attack, he committed suicide in a bathroom.

Police added that a pipe bomb found at his home was not functional.

Some Austrian media have said the young man, who has not been identified, apparently felt bullied, though police have yet to confirm this.

Austrian authorities said the suspect never completed his studies at the school.

He left a farewell note that did not reveal the motive for the attack, police said.

Franz Ruf, director general of public security, said investigations into the motive were moving swiftly.

“We don’t want to speculate at this point,” he told national broadcaster ORF on Tuesday night.

According to Ruf, there was a gap of approximately 17 minutes between the initial reports of gunshots at the school received by the police and the area being secured, ensuring there was no further danger.

Details of the attack have emerged slowly.

Austrian police said victims were found both outside and inside the school, on various floors. About a dozen people were injured in the attack, some seriously.

Austria declared three days of national mourning, with the shootings prompting a rare show of solidarity among often bitterly divided political parties.

Parents of pupils and neighbors of the school struggled to make sense of the event.

Hundreds came together in Graz’s main square on Tuesday evening to remember the victims.

Others left flowers and lit candles outside the school.

Dozens also queued to donate blood for the survivors.