PARKLAND, Fla., Feb. 14 (UPI) -- A 19-year-old who had been expelled for discipline problems walked into his former high school in a Florida suburb Wednesday and fatally shot 17 people, investigators said.
Broward County Sheriff Scott Israel said 12 people died inside Marjory Stoneman Douglas High School in Parkland, two others just outside the building, one on a nearby road and two at the hospital just before the dismissal bell.
Hours later, a bomb squad in neighboring Palm Beach County was at a mobile home containing an explosive related to the school shooting, the Palm Beach Post reported.
Sean Kelley, security supervisor for Lantana Cascade Mobile Home Park, said there was some type of explosive device at one of the residences.
"It's a horrific, horrific day," Israel told reporters in a briefing Wednesday evening near the school, where students and adults were among the dead.
Dr. Evan Boyar of Broward Health North hospital, told reporters 17 patients were transported to hospitals in the Broward Health system. Of those, eight underwent treatment at Broward Health North. Two people there died, three others were being treated for critical injuries and three were stable.
The sheriff identified the shooter as Nikolas Cruz, whom police arrested off-campus without incident.
Israel said Cruz attended the school at one time, but he was expelled for "disciplinary reasons."
When he came to the school on Wednesday, Cruz "had countless magazines," Israel said. "At this point we believe he had one AR-15 rifle."
Robert Runcie, superintendent of Broward County Public Schools, said law enforcement officials believe it was a lone shooter.
Students said they heard the school's fire alarm go off shortly before school ended for the day. They then heard a "code red" notification, an indication the school was being put on lockdown.
The Coral Springs Police Department told students and teachers to "remain barricaded inside until police reach you."
Raquel Masson Alderman said she couldn't believe it when her 10th-grade son, Matthew, texted her around 2:45 p.m. saying there might be a shooting at school. He wasn't sure if it was a drill.
"It's a parent's worst nightmare. It was surreal. It was happening, yet it didn't seem like it was. You're almost in denial, like no, this can't be happening to me and my son," Alderman told UPI late Wednesday. "He thought it was a drill but he heard gunshots and the SWAT team was there. That's when I knew: Oh, dear God, this is real.
"I told him to go to a safe place. He did. He was in a back room in the TV production room. Told him to please be safe and that I loved him."
Alderman, who co-authors the Raising Teens blog, said she wasn't able to reunite with him until about 5:30 p.m.
Local media footage of the scene showed students walking out of the building, some with their hands up in the air, others with their hands on the shoulders of the students in front of them.
Parents formed prayer groups outside the school and at a staging area in Coral Springs.
White House deputy press secretary Lindsay Walters said President Donald Trump was monitoring the situation.
"Our thoughts and prayers are with those affected," she said.
White House press secretary Sarah Sanders told reporters Trump spoke with Scott and offered federal assistance if needed.
"How could this happen in this state? This a state that is focused on keeping all of our children safe. You come to the conclusion that this is absolutely pure evil," Scott said at a 9 p.m. news conference. "My prayers are with everybody impacted."
Florida Attorney General Pam Bondi said the state will pay for funeral expenses for the victims.
Marjory Stoneman Douglas High School is "A"-rated school in an affluent suburb of Fort Lauderdale. It has an enrollment of about 3,000 students.
The school will remain closed through Friday and all school activities for the remainder of the week have been canceled. The school is providing grief counselors to students, parents and staff members, Runcie said.
Editor's note: An earlier version of this story included quotes from Sen. Bill Nelson, D-Fla., who told CNN and MSNBC the shooter was wearing a gas mask and carrying smoke grenades. On Feb. 16, Broward County Sheriff Scott Israel said this information was incorrect. Police did find a balaclava at the scene, a ski mask with cutouts for the eyes.
Charlene Pacenti contributed to this report.