Madeleine Morris describes what can be seen in new CCTV footage
There is no evidence the failed attempt to detonate a car bomb in New York was the work of al-Qaeda or any other big terrorist group, the city's mayor says.
Michael Bloomberg spoke after police dismissed claims by a Pakistani Taliban group that it was responsible.
Investigators are hunting a middle-aged white man seen removing his shirt near the scene at Times Square on Saturday evening and stuffing it into a bag.
President Barack Obama has vowed the US will track down the perpetrators.
Investigators have been gathering evidence from the Nissan Pathfinder in which the homemade petrol and propane bomb was found.
The engine was still running with hazard lights flashing when the SUV, emitting smoke, attracted the attention of a street vendor.
WHO ARE PAKISTANI TALIBAN?
A network of hardline Islamic groups threatening to destabilise Pakistan
Main faction, the Tehrik Taliban Pakistan (TTP), is led by Hakimullah Mehsud
TTP formed in 2002 when Pakistan invaded tribal areas to target foreign militants spilling across Afghan border
Blamed for a wave of suicide bombings and other attacks in Pakistan
Based in tribal areas in the north-west - main strongholds have been North and South Waziristan with links to Punjab
Police evacuated part of the bustling entertainment district and shut subway lines, while a controlled explosion was carried out.
New York City Police Commissioner Raymond Kelly said on Sunday the bomb was crude, but could have sparked a "significant fireball".
Another component of the device was a rifle cabinet packed with more than 100lb (45kg) of fertilizer, although police said it was not of a type volatile enough to explode.
Commissioner Kelly said they were looking for an unidentified white man, thought to be in his 40s, who was spotted behaving "furtively" nearby.
CCTV captured the suspect walking down an alley and changing a shirt, while looking back in the direction of the smoking SUV.
Police are also examining a home video taken by a tourist of a man seen near the car.
Detectives have established that the car's registration plates do not match up with the Nissan.
They belonged to a car owner in the state of Connecticut, who told officers he had sent the plates to a scrap-yard.
A Pakistani Taliban group claimed in a one-minute internet video that it was behind the failed attack.
Tehreek-e-Taliban said the bomb was revenge for the deaths of its leader and the leader of al-Qaeda in Iraq.
But the police commissioner and the mayor cast doubt on the claim.
"There is no evidence that this is tied in with al-Qaeda or any other big terrorist organisation," Mr Bloomberg said.
The mayor earlier told reporters New York had avoided what could have been "a very deadly event".
'Pop, pop, pop'
US Homeland Security Chief Janet Napolitano has said there was so far no evidence that it was more than a "one-off event", but added it was "a potential terrorist attack".
Police have been gathering evidence from the SUV that contained the bomb
Duane Jackson, the 58-year-old handbag seller who spotted the vehicle, has been hailed as a hero.
The Vietnam War veteran alerted a passing police officer, after noticing the car parked illegally with its keys in the ignition.
"That's when the smoke started coming out and then we heard the little pop, pop, pop - like firecrackers going out," he said.
The New York Police Department has been on constant alert since the 9/11 attacks.
Earlier this year, two men, one an Afghan immigrant, pleaded guilty to a plot to set off suicide bombs in the city's subway system.
And last year four New Yorkers went on trial accused of plotting to bomb synagogues in the city and fire missiles at military aircraft.