Umer Ahmad, a 43-year-old Muslim-American physician from New Jersey, was in his Trenton office when he heard that a rented pickup truck had deliberately driven down a bike path in Lower Manhattan, killing eight people and injuring about a dozen more.
"My initial reaction was, obviously, concern and shock over what happened," Ahmad told NBC News. "And then, basically, I was wondering if it was a Muslim who did it."
The suspect was identified as an Uzbek immigrant named Sayfullo Habibullaevic Saipov, 29, who entered the United States in 2010, law enforcement officials said.
Saipov hopped out of the truck and shouted "Allahu Akbar," or "God is great," before firing a BB or pellet gun, four senior law enforcement sources said. Law enforcement sources said he left a note in the truck claiming he committed the attack for the Islamic State terrorist group.
A police officer on patrol in the area opened fire, hitting the suspect in the abdomen and ending what New York Mayor Bill de Blasio called "an act of terror."
 Mayor Bill de Blasio: 'This Was An Act of Terror' 0:51
Ahmad's question was answered.
"My biggest concern is that he's readily identified as a Muslim and then that is extrapolated out to my own faith," he said.
In the wake of Tuesday's attack, some Muslim Americans and community leaders expressed concerns over how their religion would be perceived and whether Muslims would become targets of violence.