United States president Donald Trump has fingered mental illness after a teenager killed 17 people in a shootout at a high school in Florida.

“So many signs that the Florida shooter was mentally disturbed, even expelled from school for bad and erratic behavior,” the president tweeted.

“Neighbors and classmates knew he was a big problem. Must always report such instances to authorities, again and again!” he added.

After the attack Wednesday afternoon, Trump offered his “prayers and condolences to the families of the victims.”

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“No child, teacher or anyone else should ever feel unsafe in an American school,” he tweeted.

Trump’s tweet Thursday was not the first time he pointed a finger at mental illness in connection with a mass shooting.

In November, he described a deadly shooting at a church in Sutherland Springs, Texas, as a “mental health problem at the highest level” – not a “guns situation.”

Trump also raised the same argument after the Las Vegas shooting in October in which 64-year-old Stephen Paddock killed 58 people and injured more than 850 by firing at concertgoers at a music festival.

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