So far, what they've found is "very, very disturbing", he said.
"This has been a day where we've seen the worst of humanity", Broward County Public Schools Superintendent Robert Runcie said during a press conference on Wednesday afternoon.
Police say the gunman was armed with a semiautomatic AR-15 rifle and carried "multiple" magazines with him. Twelve were killed inside the school, two just outside and one on the street, while two other victims died from their wounds in the hospital, Israel said.
Students who knew the shooter, identified as Nikolas Cruz, described a volatile teenager whose unusual behavior had caused others to end friendships with him, particularly after the fight that led to his expulsion.
Peter Thiel considered leaving Facebook's board
Silicon Valley companies and tech workers overwhelmingly supported Democrat Hillary Clinton in the 2016 election. He was the first outside investor in Facebook and made early-stage investments in Yelp, LinkedIn, and Quora.
According to NBC, Cruz was recently expelled from the high school for disciplinary reasons, but he was enrolled in another school within the same district.
At least 17 people have been killed in a shooting at a school in south Florida on Valentine's Day. Two others died at the hospital. Footage appearing on television and social media depicts students being escorted out of the high school in small groups amid a heavy police presence.
President Donald Trump speaks at a meeting at the White House, Wednesday, Feb. 14, 2018, in Washington. Nikolas Cruz was taken into custody off-campus about an hour after the shooting.
Trump said he has spoken with Florida Gov. Rick Scott about the shooting.
Florida Congresswoman Frederica Wilson called the shooting "heartbreaking" on Twitter, sending her thoughts and prayers to the victims.
"No child, no teacher should ever be in danger in an American school", he said.