At a news conference on Sunday, Mr Kelly said the device in the Nissan Pathfinder consisted of two clocks connected by wires to a can, which they believed was the detonator, propane tanks and a gun locker.
Mr Kelly also said a white man in his 40s was seen removing a dark shirt in the area and putting it in a bag.
The commissioner added that police would shortly speak to a person in Pennsylvania who believed he may have recorded the man on a video camera.
Experts still had a huge amount of camera footage to pore over, Mr Kelly said.
"It's not easy to go through these tapes. I think we had 82 cameras in the area - we've looked at 30 of those cameras. Three of them had some value," he said.
Earlier on Sunday, US Homeland Security Chief Janet Napolitano said so far there was no evidence that it was more than a "one-off event".
But she added that it was regarded as "a potential terrorist attack".
Police study CCTV
The vehicle has been sent to a forensic lab in the city's Queens district, after police had conducted a controlled explosion to make it safe, and Times Square was reopened.
Part of the district - where many theatres are sited - had been sealed off on Saturday night after the bomb alert.
"There are forensics in terms of video or possible video that might exist. There is a lot of evidence being tracked down by a lot of people right now," Ms Napolitano said.
Both US President Barack Obama and New York City Mayor Michael Bloomberg praised the quick response by the New York Police Department.
"We are very lucky," Mr Bloomberg told reporters. "We avoided what could have been a very deadly event."
He said the bomb "looked amateurish", but could have exploded, adding that the incident was a "reminder of the dangers that we face". "We have no idea who did this or why," he said.
Police believe the intention was to ignite a fireball.
By Gordon Corera, BBC security correspondent
Authorities are being careful about assigning responsibility at this early stage.
Domestic right-wing extremists have carried out attacks in the past, including the 1995 Oklahoma City bombing which killed 168 people. But those groups usually target government buildings.
There are also some similarities to the failed 2007 attack on the Tiger Tiger nightclub in London, in which a car bomb fizzled and failed to go off. That was carried out by individuals inspired by al-Qaeda's ideology, but who had no real contact with the organisation itself. The relative amateurishness of the Times Square explosive device at least suggests a similar possibility this time.
For many years, the US expressed some relief that it appeared immune from the so-called home-grown radicalisation witnessed in the UK and Europe. But recently there have been a number of arrests and growing evidence of jihadists based in the US turning to terrorism, including some arrests in New York itself.
Correspondents say the New York Police Department is on constant alert after a series of alleged terror plots in the wake of the 9/11 attacks.
Police acted on a tip-off from a street vendor - a Vietnam War veteran, who saw smoke coming from the SUV parked on 45th Street and Seventh Avenue at about 1830 (2230 GMT) on Saturday.
The vehicle had its engine running and hazard lights flashing, officials said.
Duane Jackson, a 58-year-old handbag vendor, said he had spotted the car parked illegally and when he examined it he saw keys in the ignition with about 20 keys on a ring.
'Pop, pop, pop'
He said he alerted a passing mounted police officer.
"That's when the smoke started coming out and then we heard the little pop, pop, pop - like firecrackers going out and that's when everybody scattered and ran back," he told the Associated Press. "We dodged a bullet here," he added.
Police shut down several blocks of Times Square, as well as subway lines, while a robotic arm broke windows of the vehicle.
"There were explosive elements, including powder, gasoline, propane and some kind of electrical wires attached to a clock," police spokesman Paul Browne said.
"No motive has been identified," he added.
Police 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 junkyard.
Most Broadway shows went ahead despite the alert.
On everyone's mind is the city's darkest day, the September 2001 attack on the Twin Towers just a few miles away, says the BBC's Barbara Plett in New York.
The most recent terror alert in New York City involved a plot to set off suicide bombs in the subway system.
Earlier this year an Afghan immigrant, Najibullah Zazi, and an associate, Zarein Ahmedzay, both pleaded guilty in connection with the attempt.
Last year four New Yorkers went on trial accused of plotting to bomb synagogues in the city and fire missiles at military aircraft.
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