Updated with additional details: “The shooter wore a gas mask, and he had smoke grenades; he set off the fire alarm so the kids would come pouring out of the classrooms and into the hall, and there the carnage began,” the senior senator from Florida Bill Nelson told CNN this evening, citing the FBI as his source.

This shortly after state’s Sen. Marco Rubio tweeted authorities told him the high school gunman who murdered 17 on Valentine’s Day “designed and executed” the attack to maximize loss of life, as news networks reported an account that the gunman also was armed with an AR-15 and multiple magazines.

Authorities reported a bomb squad is combing Marjory Stoneman Douglas High School, where they believe a 19-year-old former student known to  be “into guns” and a chip on his shoulder opened fire on Valentine’s Day, leaving the 17 dead and three more in critical condition.

A suspect is in custody. Nikolas Cruz, a 19-year-old who had been expelled from the school for disciplinary reasons, was apprehended about a mile from the the campus, FNC’s Shep Smith reported.

Scott Israel, sheriff of Broward County, about an hour northwest of Miami, reported reported at least 14 victims were transported to area hospitals with varying degrees of wounds. The dead included adults and students.

Campus building are not safe to be cleared until the SWAT team on site says it’s safe and clear, he added. Students are still in the school building; Israel instructed parents looking for their child to go to a nearby Marriott, to which students are being transported as they are evacuated.

A male suspect, about 18 years old is in custody; he was apprehended without incident off campus in a nearby community, Israel said. The shooting suspect was, at various times during the shooting, outside and inside the building. He is a former student at the school.

Fox News Channel’s Shep Smith reported the suspect, who “knew the lay of the land” at the campus, was taken to a local hospital and was  “being treated for we don’t know,” and will then be taken for processing.

Previous: Robert Runcie, Superintendent Broward County Public Schools, is holding a presser to inform there have been “numerous fatalities” in the school shooting that began around 2:30 PM ET – 11:30 PM PT.

Broward Sheriff’s office tweeted at least 14 victims, meaning dead and injured:

About one hour after the shooting broke out, the sheriff’s office tweeted the gunman was in custody but scene remains active:

NBC News compiled a list of shooting incidents that have resulted in injuries and/or deaths at elementary, middle and high schools just since the beginning of 2018. As of Feb. 2, not including Wednesday’s shooting, a total of four people had been killed and 20 have been injured in school shootings.

And, Fox News Channel’s Shep Smith, meanwhile, listed every school shooting since Columbine in ’99:

White House canceled its press briefing:

From Press Secretary Sarah Huckabee Sanders:

The President has spoken with Governor Scott of Florida and offered federal assistance if needed. Department of Homeland Security Secretary Nielsen also spoke with Governor Scott as well as state and local officials. She has briefed the President on those conversations. The Governor, the Secretary, and other Administration officials will continue to keep the President updated.

In light of this tragedy there will not be a regularly scheduled briefing as previously announced. We will inform you as more information is available.

We continue to keep the victims, and their friends and family, in our thoughts and prayers.

President Trump tweeted:

TV news outlets abruptly dropped Washington-centric coverage Wednesday afternoon when a shooter attacked students and staff at Marjory Stoneman Douglas High School in Parkland, Florida on Wednesday afternoon. Quick word of at least 20 shot in the school or on the campus triggered TV news pundit talk of Columbine High School massacre of 1999 in which 12 students and one teacher were murdered, and another 24 injured, by two heavily armed students who then committed suicide.

Cable news networks showed helicopter footage of ambulances swarming the area, victims being tended to on sidewalks, and a SWAT team heading with weapons drawn toward the high school attended by about 3K students. Dozens of teens could be seen running or walking from the building, some with hands raised over their heads to signal they did not have a weapon.

More than an hour after first reports of the shooting, local sheriff tweeted to warning the gunman, who had shot into the school from outside the building, still was at large:

Multiple students interviewed on CNN said students began running out of the building after someone pulled a fire alarm in the school about 10 minutes before end of school day; one reported they were told over the school’s intercom system to evacuate the building. As they exited, shots were heard,  students told the network affiliate’s reporter.

One distraught mother marveled the network the city had just been named safest place to live in Florida.

White House said President Donald Trump had been alerted:

From Deputy Press Secretary Lindsay Walters:

The President has been made aware of the school shooting in Florida. We are monitoring the situation. Our thoughts and prayers are with those affected.

Developing story………