Investigators flooded what is typically a bustling Chelsea street Sunday, sifting through shards of glass, metal shrapnel and assorted debris in a search for clues pointing to the culprit of the bombing that injured 29 people and rocked one of New York’s upscale neighborhoods.

“Think of a jigsaw puzzle out in the street right now," said NYPD Chief of Detectives Robert Boyce of the crime scene on West 23rd Street.

A source told Metro New York that the police acquired reliable footage from only two security cameras at businesses on the block between 6th and 7th avenues: one that faced directly at the site of the explosions which took place at around 8:30 p.m. Saturday, and one from a much greater distance.

An un-detonated pressure-cooker bomb found in a trash can on 27th Street a few hours after the explosion might be the best hope of finding such evidence as fingerprints and fibers. Reports describe the improvised explosive device as having wires protruding from it and a cellphone attached with silver electrical tape.

"Do we think they're related? Yes, we have to move in that direction, but right now we're not ready to make those calls yet," Boyce said of the device.

There is also some suspicion that a pipe-bomb explosion along the boardwalk in Seaside Park, New Jersey, on Saturday is connected to the New York incident. There were no injuries reported from that incident and police have not confirmed any evidence connecting the blasts.

The FBI, ATF and the state police are assisting local police in the investigation. Physical evidence, including the pressure-cooker bomb, was sent to an FBI lab in Quantico, Virginia. 

All 29 people injured in Chelsea were taken to local hospitals and released by 11 a.m. Sunday, many having been treated for flesh wounds from shrapnel that flew into their faces and arms.

Restaurants and businesses in the surrounding area were open Sunday, but many people remained shaken by the previous night’s mayhem.

Alexandra Tucto, a salesperson at the Chelsea Kennel Club said she was standing right outside the store when the explosion happened. “The dogs definitely react to loud noises and this was a really huge boom,” she said. “And all the dogs on the street were barking.”

Tucto and her friend were waiting for a taxi when they heard and felt the explosion. “We felt the heat of the big whoosh. I smelled fumes. We got so scared we just kept running,” she said.

Leo Calderon, who also works at the kennel club, said the explosion brought back memories of 9/11 when he was 13 and attending school very close to the World Trade Center.

“The boom, the chaos, the sirens… immediately brought me back to that moment. I’ll always be traumatized. That day terrorism defined my life so when something like this happens it feels like fate,” he said.

The motive of the attack is undetermined, officials said, though investigators were examining an online blog written by someone claiming to be responsible for the bombing.

“We have a lot more work to do to be able to say what kind of motivation was behind this," Mayor Bill de Blasio told reporters Sunday. "Was it a political motivation? Was it a personal motivation? We do not know that yet."

The mayor said security measures will be increased at key locations around the city in the wake of the bombing. He noted that law enforcement will be particularly focused at the United Nations building in light of the scheduled session this week of the General Assembly.

“You will see a very substantial New York Police Department presence this week,” De Blasio said. “The biggest ever.”

The mayor asked citizens to be watchful and report any suspicious activity to local authorities.

“Be vigilant,” he said.

Vincent Stanhope, who was at his apartment in the nearby Flatiron district said the boom so loud that it set off car alarms for blocks. He said the incident reminds him of how vulnerable we all are no matter how upscale the neighborhood.

“It’s terrorism, it’s reality and it’s here to stay.”