President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE issued a proclamation on Thursday mourning the deadly shooting at a high school in Parkland, Fla., and ordering American flags to be flown at half-staff.

"Our Nation grieves with those who have lost loved ones in the shooting at the Marjory Stoneman Douglas High School in Parkland, Florida," the proclamation reads.

The proclamation calls on all U.S. public buildings, military outposts, embassies and the like to fly their flags at half-staff through Monday.

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The shooting at Marjory Stoneman Douglas High School, roughly 25 miles north of Fort Lauderdale, left 17 people dead on Monday.

The suspect, identified as Nikolas Cruz, 19, a former student at the school, was arrested after fleeing the scene. He was charged Thursday morning with 17 counts of premeditated murder.

Trump suggested in a tweet on Thursday that Cruz was "mentally disturbed," pointing to the fact that he was expelled from the school for disciplinary issues.

"So many signs that the Florida shooter was mentally disturbed, even expelled from school for bad and erratic behavior. Neighbors and classmates knew he was a big problem," Trump tweeted. "Must always report such instances to authorities, again and again!"