Thousands of people have reacted to the news of a former student suspected of killing at least 17 people at Marjory Stoneman Douglas High School in Parkland, Florida.

The president, U.S. lawmakers, alumni of the high school and other celebrities expressed their thoughts on social media after Wednesday’s shooting.

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Related: Former student opens fire at Florida high school, killing 17

More: Suspect in fatal Florida school attack is former student with 'anger' issues

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Timeline: South Florida school shooting as developments unfolded

Watch: Florida senators respond to mass school shooting