NEW YORK — A bomb that injured 29 people Saturday in the Chelsea neighborhood of Manhattan, and another that failed to detonate, 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.
Both bombs appeared designed to create maximum chaos and fatalities — they also provided a trove of clues even as any suspects remained unnervingly at large.
A top law enforcement official said pressure cookers were filled with “fragmentation materials.” The bomb that exploded, at 23rd Street, was filled with small bearings or metal BBs. A second device on 27th Street that did not explode appeared to be filled with the same material, the official said.
Late Sunday, two senior law enforcement officials said there was a “person of interest” in the bombing, but it was unclear if that person had been identified.
Senior law enforcement officials also said that they were increasingly focused on the possibility that 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.
Officials said they did not know of any motive — political or social — for any of the attacks. Early Sunday, Governor Andrew M. Cuomo said “there is no evidence of an international terrorism connection with this incident,” noting that no international terrorist group has claimed responsibility.
The search for the person or people behind the attack in New York took on added urgency as President Obama and leaders from around the world travel to New York for the UN General Assembly this week.
Tests showed that the explosive material in the 23rd Street bomb was similar to a commercially available compound called Tannerite, according to two law enforcement officials. It was unclear why Cuomo and Mayor Bill de Blasio dismissed with such certainty a tie to international terror. Experts said the bomb’s construction offered conflicting clues.
It is made by combining ammonium nitrate and aluminum powder, is frequently used in exploding targets at firearms ranges, and has rarely been used in improvised explosive devices in the United States. But the materials are easy to buy because each one on its own is not an explosive.
At the same time, pressure cookers have been a container of choice for many improvised explosive devices over the years. They were used in the deadly Boston Marathon bombings in 2013 based on a model in publications put out by Al Qaeda’s affiliate in Yemen.
An expert on IEDs used by terrorists around the world said that a device constructed with a cellphone as a timer and Christmas lights as an initiator would indicate a higher-than-average competence than is usually found in the United States. “Most of what we see in the United States is a pipe bomb with black powder or smokeless powder or a simple hobby fuse,” said the expert, who spoke on the condition of anonymity because he does sensitive work for government agencies. “This would be the high-end of sophistication for IEDs in the United States.”
The recovery of the second device provides investigators with a host of potential leads, from the phone and other materials inside the homemade bomb to the pressure cooker itself — including possibly determining when and where it was purchased — to any possible fingerprints on the device, its components or the tape that held it together.
Cuomo said he was ordering an additional 1,000 New York State Police officers and National Guard members to be dispatched to major commuter hubs, and de Blasio said New Yorkers should expect to see a heightened police presence throughout the city, including additional patrols by the city’s heavily armed counterterrorism units.
The police continued to search the area around the blast site and fanned out across the city chasing leads and trying to sort through a variety of claims of responsibility — from Twitter to websites to 911 calls — most of which were dismissed as unrelated.
Late Sunday, FBI agents were seen tearing apart the car of an Uber driver, who said the law enforcement officials were searching for possible evidence related to the attack.
The bomb was placed under a Dumpster made of heavy-gauge steel, and was powerful enough to catapult the metal box across the street.
The 29 people who were wounded mostly suffered cuts and abrasions and had all been released from the hospital by Sunday morning.
Police Commissioner James O’Neill said the unexploded device was found by two state troopers as they walked down 27th Street after calls to 911 alerted the police to a suspicious device. It was taken to be examined by bomb technicians at a police facility in the Bronx.
At first the technicians tried to peel apart the device to see its components and whether it has signature properties that can link it to the kind of device used by terrorists in the past.
The remnants of the device that exploded in Chelsea were sent to the FBI’s bomb lab in Quantico, Va., along with the improvised explosive device found in New Jersey.
While government officials had initially been dismissive of a link between the New Jersey and New York attacks, evidence from the crime scenes seemed to lead them to change their thinking.
The New Jersey blast took place 11 hours earlier when an improvised device exploded in a garbage can near the course of a charity race. That device went off around 9:30 a.m. near the boardwalk in Seaside Park, according to the Ocean County sheriff, Michael G. Mastronardy. Only one of the three pipe bombs detonated and no one was injured.
Officials said the explosive in that device appeared to be black powder. The race, the Seaside Semper Five, a 5-kilometer run that raises money for members of the Marine Corps and their families, was canceled.
The police were reviewing surveillance video in New York and New Jersey and continued to look 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.
Moments after the blast, the police swarmed Chelsea’s streets, and messages flew fast and furious from people across a city that has taken on a wary resignation that terrorism is a sad fact of life.
The Dumpster where the bomb exploded was being used in the renovation of the fifth and sixth floors of an apartment building that provides affordable housing for the visually impaired and disabled, its managing agent, Tony Savarese, said.
Savarese said the Dumpster sat on the eastern side of the building and the bomb exploded with enough force to shatter windows, break a door frame and obliterate a security camera perched above the entrance. The camera recorded little more than a blinding flash.
Savarese said he had gotten no reports of injuries among the building’s residents, but said its management was still checking on their well-being. “We have been going apartment to apartment checking on everybody,” he said.