Authorities say 27-year-old Akayed Ullah is charged on five federal terrorism counts, including use of a weapon of mass destruction and bombing a place of public use.
The charging document said law enforcement personnel found a 9-volt battery inside Ullah's pants pocket, wires connected to the battery running under his jacket and fragments of metal pipe. There was also a remnant of what appeared to be a Christmas tree light bulb attached to the wires.
According to the document, Ullah made statements indicating he "was inspired by ISIS to carry out" the attack. He said: "I did it for the Islamic State."
Related: What we know about terror suspect Akayed Ullah
Ullah built the pipe bomb in his Brooklyn residence a week before the attack and began compiling materials two to three weeks earlier, investigators said. He filled the bomb with metal screws, which he believed would cause maximum damage. On Facebook the morning of the attack, authorities say Ullah posted a statement: "Trump you failed to protect your nation."
According to the charges, one of Ullah's goals was to terrorize as many people as possible, and he chose to carry out the attack on a workday because he believed that there would be more people.
"As thousands came into New York City through the Port Authority Bus Terminal, one man came with a hate-filled heart and an evil purpose," Acting U.S. Attorney Joon Kim said.
Kim said a search of Ullah's Brooklyn apartment revealed metal pipes, pieces of wires and metal screws consistent with the bomb materials recovered at the scene.
The suspect "was an individual who flew below the radar, did not give us any indication, and he committed this act," NYPD Chief of Counterterrorism James Waters said.
While his pipe bomb was not ultimately successful, "he did follow some of the instructions that you can find readily online, unfortunately, to create such a device. A Christmas light bulb is one of those components," Waters said.
Commuters returned to the Port Authority Bus Terminal Tuesday morning as crews cleared away plywood that blocked the passageway after the explosion that left five people with minor injuries.
The 42nd St. tunnel connecting 8th and 7th Ave subway lines is back open, less than a day after a terrorist tried to set off a suicide bomb. Visible police presence. #ABC7NY pic.twitter.com/yUN9djNs2q— Derick Waller ABC7NY (@wallerABC7) December 12, 2017
Among the millions of New Yorkers back on the subway Tuesday was Jeh Johnson, Secretary of Homeland Security under President Obama.
"We're resilient and we come back strong every time after something like this happens, and I think it's important for people to see that we refuse to be terrorized," Johnson said. "This is the environment in which we live, terrorist inspired attacks by the so-called lone wolf."
Investigators say Ullah detonated his crudely-made pipe bomb, which was affixed to his chest with Velcro straps and Zip-ties, in the passageway between subway lines that runs a full city block under 42nd Street between 7th and 8th avenues. But the bomb was not packed tightly enough and failed to detonate, only blowing the ends of the pipe. Because it was strapped to Ullah, the assumption is that he had been prepared to die a suicide bomber.
Ullah told investigators he was radicalized while reading ISIS propaganda online.
"No law enforcement agencies had any information on him, he decides to make his own device," former NYPD Commissioner Ray Kelly said.
Terrorism experts say the location he chose for his attack is peculiar, but Ullah told investigators he picked the passageway because of its Christmas-themed posters. He said he was inspired to act in retaliation for US airstrikes on ISIS targets in Syria and around the world.
"New York has seen in many quarters, certainly in ISIS quarters, as being the capital of the world," Kelly said. "So you're going to make a statement in New York that's going to reverberate around the world."
Ullah is from Bangladesh and has been in the United States for seven years. He came to the U.S. on an F-4 visa, a preferential visa available for those with family in the U.S. who are citizens or permanent residents, and officials believe he planned the attack for about a year.
Authorities used his MetroCard to track his movements. They say he boarded the F train at the 18th Avenue station in Borough Park at 6:25 a.m. and took to the Jay Street station in Downtown Brooklyn, where he switched to the A for the ride to the Port Authority.
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It was the first bomb blast in the subway in more than two decades. The last bomb to go off in the subway system was believed to be in December 1994, when an explosive made from mayonnaise jars and batteries wounded 48 people in a car in lower Manhattan.
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