He looked like just another straphanger, traveling from Kensington, Brooklyn, into Manhattan. But authorities claim his intentions were to terrorize, and even kill, his fellow commuters. Now, because of widespread security surveillance, with thousands of public and private security cameras on the streets, and in subway stations and apartment buildings, it’s possible to witness the journey he took on that frightening day.

Last Dec. 11, cameras tracked Akayed Ullah, a Bangladeshi immigrant who the authorities said had strapped a homemade pipe bomb to his chest, from his Brooklyn apartment, onto the subway and into Manhattan, where he detonated his device in a crowded passageway between the Times Square and Port Authority stations. It was the first attempted suicide attack in New York since Sept. 11, 2001.

Mr. Ullah, 28, is now on trial in federal court in Manhattan, where prosecutors have presented the video captured of his journey as evidence against him. His defense claims Mr. Ullah was only trying to harm himself.