New York (CNN) — A Columbia University professor who wrote about hate crimes against Sikhs may have become a victim of one himself when 12 to 15 people attacked him while shouting anti-Muslim slurs, police said.

Prabhjot Singh, a Sikh and a professor of international and public affairs, said the attackers were yelling “get Osama” and “terrorist” when they swarmed him Saturday night near Central Park in New York.

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The professor co-wrote a 2012 op-ed for The New York Times, saying “the legacy of anti-Sikh violence and its contemporary prevalence make it painfully obvious that anti-Sikh violence is often purposeful and targeted.” He called for the government to start tracking hate violence against Sikhs specifically, instead of categorizing such instances as anti-Islamic hate crimes like the FBI generally does.

More: Sikh Professor Beaten in Possible Hate Crime in New York