As the murderous rampage that left 14 dead in San Bernardino, California, was taking place on Wednesday, Muqtedar Khan was monitoring comments by American Muslims on social media.
Those comments expressed grave concerns about the killers' religion.
"Some of the posts read: 'I pray that the killers are not Muslim,' " said Khan, who teaches at the University of Delaware.
When the shooters — Syed Rizwan Farook, 28, and his wife, Tashfeen Malik, 27 — were identified as Muslims, the postings registered a sense of fear.
"One woman wrote (on Facebook) that she was afraid to wear her hijab (a veil worn by some Muslim women that covers the head and chest) outside," said Khan. "Within a few hours, she had 12,000 'likes.' "
The likes indicate similar fears by other Muslims.
Khan, an associate professor of political science and international relations at the University of Delaware, is a visiting scholar at the Islamic Community Center of Lancaster, where he gave a talk about justice and the oppressed Friday afternoon. He has written extensively about Islam and has been featured on CNN International, FOX, BBC and other media outlets.
Until recently, Khan said most Muslim Americans were not worried about living in the United States.
But the Syrian refugee situation and the massacres in Paris and San Bernardino have raised tensions.
"The climate in the United States in the past three months has become very hostile," he said.
He attributes some of that hostility to what is being said on the presidential campaign trail.
"Republican candidates are saying this is a war," he said. That has ramped up the anti-Muslim rhetoric on social media sites as well, he said.
Khan said many Muslims believe federal legislation restricting Syrian refugees from entering this country that passed the U.S. House of Representatives is, in fact, aimed at Muslims.
The irony, he said, is that France, which has suffered two major terrorist attacks this year, has said it will accept 30,000 Syrian refugees. Germany already has accepted nearly 40,000 Syrians and and Sweden continues to accept Syrian refugees.
Despite the shrill rhetoric on the Republican campaign trail, Khan, who was born in India but has lived in this country for he past 23 years, said the backlash against Muslims in the United States has not turned to violence.
Mukaram Syed, a business consultant and member of the community center's board of trustees, said the shootings in California do affect Muslims here.
"Our children go to school with other children who know they are Muslim," he said. "It hits home."
As for those who commit acts of terrorism, Syed said the person's religion is irrelevant.
"Treat them like a criminal," he said.