The Marist College campus in Poughkeepsie, N.Y. (John Greim/LightRocket via Getty Images)

A person was arrested for making threats on social media against black students at Michigan Tech University, and a threat on Twitter shut down Marist College as police investigated.

Racial and other tensions were particularly high on many campuses across the country this week in the wake of a high-profile protest in Missouri that upended a university system.

Anonymous posts on social media only intensified those tensions, as people traded opinions they might not share publicly — and, in some cases, made threats.

Many Howard University students stayed in their rooms Thursday, frightened by an online threat that included the line “After all, it’s not murder if they’re black,” and referred to protests in Missouri.

[Threats rattle Howard U.]

That followed violent threats on the anonymous social media app Yik Yak at the University of Missouri earlier in the week.

[Two people arrested in social-media death threats directed at Mizzou]

Protests at the University of Missouri over the administration’s response to racial and bias incidents on campus forced the chancellor and the university system president to resign Monday.

Marist College reopened Friday afternoon, with afternoon classes still canceled; the small liberal-arts college on the banks of the Hudson River in upstate New York shut down Friday morning after online threats.

The Town of Poughkeepsie Police Department issued a statement Friday morning:
“At approximately 6:00am on Friday November 13, 2015 the Town of Poughkeepsie Police Department was notified by the Marist College Office of Safety & Security that an online threat was sent out via Twitter against Marist College.”

In the afternoon, police announced that they had arrested a 16-year-old boy who lives in Poughkeepsie, who posted two tweets that did not involve racial issues but were theatening to the campus.

A police investigation determined that the threat was not legitimate, and the suspect acted on his own.

On social media, some people shared this message, but there was no confirmation that this was what police were investigating.

At Michigan Tech, the university announced Friday, “Based on information from Yik Yak and Michigan Tech Information Technology, a suspect in Thursday’s social media threat was taken into custody late Thursday night and is currently lodged in Houghton County Jail.”

“It’s important to remember that we are a community and will not tolerate threats to any member of our family,” Michigan Tech President Glenn Mroz said in a statement to the campus community. “It’s time we watch out for one another.”

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