– The morning after the worst high school shooting in American history unfolded in the Broward County suburb of Parkland, parents, police, grief counselors and students at Marjory Stoneman Douglas High struggled to make sense of a massacre that killed 17 people and injured at least 15.

This is the United States’ 18th school shooting this year, and once again a community asked itself familiar questions: How did everyone miss the signs that the suspected shooter was deeply troubled, especially given his ominous postings to social media? And what could be done differently to prevent such a tragedy from happening again?

Speaking on National Public Radio early Thursday, Broward Mayor Beam Furr suggested that the shooting could have been prevented.

“We missed the signs,” said Furr, a former teacher, adding that the suspected shooter, Nikolas Cruz, had been receiving mental health counseling. “We should have seen some of the signs.”

“We have to be more vigilant,” Michael Udine, a Broward commissioner and former mayor of the city where the massacre unfolded, also told NPR. “If this can happen in a city like Parkland, it can happen anywhere.”

Speaking on WIOD-610 AM radio Thursday morning, Broward Sheriff Scott Israel called for lawmakers to give police more authority to confine individuals who exhibit disturbing behavior that may threaten others. He said Cruz had posted troubling photos and videos on social media.

“We saw a pic yesterday where he took a chameleon and he splattered the chameleon,” Israel said. “Things like this, that’s not normal behavior. Someone needs to have the empowerment, if you see something like this, to go over and say, ‘You know what we’re worried. We’re concerned about you. We’re concerned about our citizens. We’re concerned about our children.’ Somebody has to stand up for them and say we need to evaluate you.”

Israel noted that Cruz used a familiar weapon that has surfaced time and again after mass shootings, from Sandy Hook Elementary School in Connecticut, where 20 children were killed in 2012 to the Orlando nightclub shooting in 2017 to the Las Vegas concert shooting last fall: the AR-15, a semiautomatic assault rifle.

“How easy was it for him to get this weapon? These are things that have to be considered,” Israel said, adding that many assault weapons are ordered online and delivered to the buyer 80 percent complete, which is allowed by law. He said the buyer then finishes building the gun, which is frequently not traceable.

“It takes hours,” Israel said. “It’s nothing that you need some incredible skill to do and now the person has a gun with no serial number.”

Cruz, a former student at Douglas High, was booked into the county jail Thursday morning after prosecutors charged him with 17 counts of premeditated murder.

Police had arrested Cruz on Wednesday after he attempted to blend in with students fleeing the scene. Cruz was wearing a military uniform from his JROTC class, according to one witness, and Broward Sheriff’s Office deputies said they were able to track his movements using the school’s video surveillance.

Jonathan Guimaraes, 17, a senior at Douglas High, said he knew Cruz from their JROTC class last year.

“He was quiet, nice,” Guimaraes said. “That’s how he was able to blend in. He was wearing his JROTC uniform.”

One teacher, who asked not to be identified, said he had locked his students in a classroom and that he could hear a police radio outside the locked door. At one point, the teacher said he heard Cruz’s name and a police officer say the suspected shooter might be headed toward the middle school nearby.

When the shooting was over, police said, 12 people had died inside the school building, 2 died outside, one died on the street, and two in an area hospital. The injured were taken to Broward Health North in Pompano Beach and Broward Health Medical Center in Fort Lauderdale.

As the gravity of the prior day’s shooting settled in, grief counselors on Thursday fanned out to area parks, schools and libraries to help students, families and teachers cope with the tragedy.

Students who left their bookbags, Teddy bears and Valentine’s Day gifts behind in the scramble to flee the shooting were allowed to return Thursday to collect their belongings.

Broward officials also offered more details of the deadly rampage. Broward County Schools Superintendent Robert Runcie said the school remained an active crime scene, and that the bodies of some of the dead had not yet been removed.

Runcie added that fire alarms at the school had been tripped by gun smoke from the assault weapon that Cruz allegedly used — and not by Cruz himself, as had been reported previously.