NEW YORK -- With no international terrorist group claiming responsibility for a powerful explosion Saturday night in Manhattan, authorities on Sunday combed through surveillance videos, interviewed eyewitnesses and sifted through remnants of the bomb for clues into an attack that left dozens wounded.
The New York Police Department, joined by the FBI, mounted a large-scale hunt for the person or people behind the attack, which injured 29 people in the Chelsea neighborhood of Manhattan.
Agents with the FBI pulled over "a vehicle of interest in the investigation" on a highway in Brooklyn on Sunday night and were questioning the vehicle's occupants, according to FBI spokesman Kelly Langmesser.
She wouldn't provide further details, but a government official and a law enforcement official who were briefed said five people in the car were being questioned at an FBI building in lower Manhattan. The officials spoke on condition of anonymity because they were not authorized to speak about the ongoing investigation.
No one has been charged with any crime, and the investigation is continuing, Langmesser said.
Four blocks from the blast site, authorities on Saturday found and removed what they described as a second device. Gov. Andrew Cuomo said the devices appeared to be similar in design, and one federal law enforcement official who agreed to speak about the continuing investigation only on the condition of anonymity described it as a "viable device" that failed to detonate.
The New York Police Department conducted a controlled detonation of the second device at a police facility in the Bronx on Sunday evening.
Both bombs were filled with shrapnel and made with pressure cookers, flip phones and Christmas lights that set off a powerful explosive compound, law enforcement officials said Sunday evening, adding the bombs appeared designed to create maximum chaos and fatalities.
The Manhattan bomb contained residue of Tannerite, an explosive often used for target practice that can be picked up in many sporting goods stores, a federal law enforcement official said Sunday.
On Sunday night, investigators examined a suspicious device found in a trash can near a train station in Elizabeth, N.J., that forced the suspension of service on the busy Northeast Corridor line.
Elizabeth Mayor Christian Bollwage said two men called police and reported seeing wires and a pipe coming out of the package after finding it about 9:30 p.m. Sunday.
The investigation into the New York attack took on added urgency as President Barack Obama and leaders from around the world headed to New York for the annual U.N. General Assembly meeting this week.
New York Mayor Bill de Blasio said security would be stepped up across the city.
Cuomo said there did not appear to be an ongoing threat to the city, but that in an abundance of caution, he ordered an additional 1,000 State Police officers and National Guard members to be dispatched to major commuter hubs.
Cuomo added that the explosion did not appear to be linked to international terrorism, but that it was a powerful bomb designed to kill.
"This is one of the nightmare scenarios," he said at a news conference Sunday. "We really were very lucky that there were no fatalities."
Senior law enforcement officials also said Sunday that they were investigating whether the attack was connected to a bombing that took place Saturday morning in New Jersey, but the authorities still needed to compare all the bombs before drawing any conclusions. There, three pipe bombs were tied together, placed in a trash can and also employed by a flip phone as a timing mechanism, according to officials.
The New Jersey blast took place 11 hours earlier, when the bomb exploded near the course of a charity race that was about to start in a small town on the Jersey Shore. That device went off around 9:30 a.m. Eastern time near the boardwalk in Seaside Park, according to the Ocean County sheriff, Michael Mastronardy. The race, the Seaside Semper Five, a 5-kilometer run and charity event along the waterfront that raises money for members of the Marine Corps and their families, was canceled.
Cellphones were discovered at the sites of both bombings, but no Tannerite residue was identified in the New Jersey bomb remnants, in which a black powder was detected, officials said.
Officials noted that there had been no claim of responsibility from any terror network. In contrast, the Islamic State was quick on Sunday to claim a stabbing attack at a Minnesota shopping mall Saturday night that left nine people injured.
Cuomo said the explosion of the Manhattan bomb -- which was placed under a dumpster made of heavy gauge steel -- was so strong that it caused extensive property damage on both sides of the street. The mangled dumpster remained roped off by crime-scene tape as store owners and residents slowly filtered back into the area.
Police were reviewing surveillance video and continued to scour the area for clues while trying to understand the choice of location for the bomb: pointedly not Times Square, a commuter hub, train or landmark, which have been targets of terrorism in the past.
The nondescript area -- a sidewalk, near some Dumpsters in a residential area of Chelsea -- held its own significance.
"You've got to go somewhere," said a New York law enforcement official who agreed to speak about the continuing investigation only on the condition of anonymity. "So the question is: Is the location significant, in terms of motive? And we don't know that 23rd Street has any particular significance."
Moments after the blast, police swarmed Chelsea's streets, which reverberated across a city scarred by terrorism and vigilant about threats just days after the 15th anniversary of the Sept. 11 attacks.
Luke McConnell, who was visiting from Colorado, was headed toward a restaurant on West 27th Street when the blast occurred.
"I felt it, like a concussive wave, heading towards me. Then there was a cloud of white smoke that came from the left side of 23rd Street near Sixth," McConnell said. "There was no fire, just smoke."
Information for this article was contributed by Marc Santora, William K. Rashbaum, Al Bake, Adam Goldman, C.J. Chivers, Sandra Garcia, Christopher Mele, Sarah Maslin Nir and Nate Schweber of The New York Times and by Jake Pearson, Alicia A. Caldwell, Karen Matthews, Maria Sanminiatelli, Michael Balsamo, Dake Kang, Eric Tucker and Kevin Freking of The Associated Press.
A Section on 09/19/2016