Authorities in Florida could offer no explanation Wednesday night as to why a 19-year-old former student armed with an AR-15 rifle opened fire at a high school earlier that day, killing at least 17 people and wounding more than a dozen others. Broward County Sheriff Scott Israel identified the gunman as Nikolas Cruz, a former student at Marjory Stoneman Douglas High School in Parkland, a city of about 30,000 people, located 50 miles (80 kilometers) north of Miami. The student had been expelled for "disciplinary reasons," but was currently enrolled in Broward County Public Schools. Cruz, whose fellow students described him as "troubled," was arrested without incident in the nearby town of Coral Springs after the rampage and taken to hospital with minor injuries, the sheriff said. "We have already begun to dissect his websites and things on social media that he was on and some of the things... are very, very disturbing," Israel said. "If a person is predisposed to commit such a horrific event by going to a school and shooting people ... theres not anybody or not a lot law enforcement can do about it." Israel said both students and adults had been killed, 12 of whom have now been identified. He said at least 14 were taken to hospital and two had died there of their wounds. He added one of those killed was a football coach, and one student injured was a deputy sheriffs son. The shooting, one of nearly 20 at a school since the start of the year, will once again throw the spotlight on the epidemic of gun violence in the United States, where there are 33,000 gun-related deaths annually. But when questioned at a press conference late Wednesday, Florida Governor Rick Scott -- who described the massacre as "just pure evil" -- declined to make a statement on gun control in the aftermath of the shooting.