Judy Woodruff: Two weeks before Christmas, residents and workers in New York City experienced another frightening moment. An explosion occurred in a passageway in the subway near the Port Authority bus terminal. The would-be suicide bomber left at least three people with minor injuries. William Brangham reports.

Man: At approximately 7.20 this morning, we had a terror-related incident.

William Brangham: Emergency crews swarmed the streets near Times Square this morning after a man detonated a homemade pipe bomb in the subway.

Man: It's the guy in the hoodie.

William Brangham: Here, cell phone video of a Port Authority surveillance monitor purports to show the moment the assailant set the bomb off. A finger points out the alleged assailant among the commuters, and then a blast and a burst of smoke. Left behind, a single body sprawled on the ground. The attacker was taken to a local hospital with minor burns. Elsewhere in the packed station, the blast created a panic during rush hour.

Alicja Wlodkowski: Suddenly, I see a group of people, like sixty people, running like nuts.

William Brangham: New York City Mayor Bill de Blasio said the city had avoided a major catastrophe.

Mayor Bill De Blasio: Let's be also clear this was an attempted terrorist attack. Thank God the perpetrator didn't achieve his ultimate goals.

William Brangham: Law enforcement officials identified the suspect as 27-year-old Akayed Ullah. They say he is originally from Bangladesh and they say he was inspired by, but perhaps did not have direct contact with, the Islamic State group. White House spokeswoman Sarah Sanders today said Ullah was here on what's called an F-43 visa, one of many that's granted to foreign relatives of U.S. citizens, and part of a program President Trump wants to curtail.

Sarah Sanders: We know that the president's policy calls for an end to chain migration, which is what this individual came to the United States through. And if his policy had been in place, then that attacker wouldn't have been allowed to come in the country.

William Brangham: Authorities say the bomb was a low-tech explosive device strapped to the attacker's body with velcro and plastic ties. The New York Times reported the suspect apparently said he chose the subway because of its Christmas-themed posters. At Ullah's home in Brooklyn, police looked for clues into his background and motive. For the PBS NewsHour, I'm William Brangham in New York.