President Donald Trump reacted to the shooter who is suspected of killing 17 students at a Florida high school.

“So many signs that the Florida shooter was mentally disturbed, even expelled from school for bad and erratic behavior,” Trump wrote on Twitter. “Neighbors and classmates knew he was a big problem.”

The suspected shooter was reportedly treated for mental problems at a local clinic and expelled from school for threatening students and demonstrating abusive behavior.

Law enforcement officials said that the shooter demonstrated “very, very disturbing” behavior on social media and the FBI was reportedly told of a comment under a YouTube account with his name about being a “professional school shooter.” The account was deleted by YouTube on Wednesday night. The shooter’s Instagram account featured images of guns, according to reports.

Before he was expelled, Former teachers and students said that the shooter was suspended in school for having bullets in his backpack and that teachers were warned that he was not allowed on campus with a backpack.

Trump urged friends and families to report problematic students to law enforcement.

“Must always report such instances to authorities, again and again!” he wrote.

Trump offered prayers and condolences on Twitter on Wednesday after news broke of the deadly shooting.

“My prayers and condolences to the families of the victims of the terrible Florida shooting. No child, teacher or anyone else should ever feel unsafe in an American school,” he wrote. “We are working closely with law enforcement on the terrible Florida school shooting.”

Wednesday’s White House press briefing was canceled after several delays and the president did not address the country after it was clear that multiple casualties occurred.

My prayers and condolences to the families of the victims of the terrible Florida shooting. No child, teacher or anyone else should ever feel unsafe in an American school. — Donald J. Trump (@realDonaldTrump) February 14, 2018