At least 10 people, including the gunman, were killed Tuesday at an adult education centre in what Sweden’s prime minister called the country’s worst mass shooting. But a final death toll, a conclusive number of wounded and a motive hadn’t yet been determined hours later.

Over a year ago, tips about online threats led Georgia police to question a 13-year-old boy, but there wasn't enough evidence to arrest him. On Wednesday, he opened fire at his high school near Atlanta, killing four and wounding nine, officials reported.