How NYPD cracked the Saturday night bombing? With help from two gentlemen-thieves!

New York police have zeroed in on an Afghan-American, Ahmad Khan Rahami, 28, as the man behind the bomb that went off on Saturday night in Manhattan, injuring 29 people, and another unexploded device that they accidentally found four blocks away.

Now, it turns out, that lucky accident of finding the second device -- an explosive mounted inside a pressure cooker -- happened, thanks to two 'thieves' -- or more accurately, as the New York police have said, two men who, from CCTV footage, looked like two well-dressed gentlemen who were walking by, found a rolling suitcase, opened it, took out the pressure cooker, left it on a garbage dump, and walked away with the suitcase!

The two 'gentlemen', according to reports on Reuters and on New York-based DNAinfo.com, did not bother to look inside the pressure cooker, despite wires sticking out of it, and left the cellphone that had been placed inside as the triggering mechanism, intact. The cellphone is what led New York police to the family of Rahami.

The two men, caught on surveillance video footage, are considered potential witnesses, not suspects, in the bombing, Reuters quoted Robert Boyce, chief of detectives for the New York City Police Department.

"They looked like they were two gentlemen just strolling up and down Seventh Avenue at the time. We have no information that would link them to this at all," Boyce said at a briefing. "However, we still want to talk to them, obviously."

Boyce said the two men were seen picking up the bag containing the device, removing it and then leaving with the bag, for reasons that remains unclear.

"Once they picked up the bag, they seemed incredulous they had actually picked this up off the street and they walked off with it," Boyce said. "So we'll find out, we'll put their images out. Hopefully we can get them identified."

Earlier on Monday, Rahami was arrested, following a gun battle with police, for the New York bombs as well as one that exploded in a New Jersey beach town on Saturday. On Sunday, five more devices were found in Elizabeth, the suspect's hometown.

Rahami's arrest was due to another lucky break for the police in Linden, New Jersey, which neighbours Elizabeth, about 20 miles west of New York. Harinder Bains, the owner of Merdie's Tavern in Linden, called up the police after he found Rahami sleeping in the doorway of his bar. Bains had recognised Rahami from the pictures he had seen on television.

When an officer woke the sleeping man, Rahami pulled out a gun, fired a bullet into the officer's bullet-proof vest, and tried to escape. The officer pursued Rahami who continued to fire off shots behind him, hitting a patrol car and grazing an officer inside. Responding police shot Rahami and took him into custody Monday morning.

Came back a changed man from Afghanistan

Rahami was "always friendly. This is really shocking", his friend Flee Jones, 27, told DNAinfo.

He lived with his father, sister and three brothers in Elizabeth, New Jersey, and the family owned and operated a local restaurant, First American Fried Chicken. Jones said he and his family often received free meals from Rahami's father when they didn't have enough money to pay for food.

Jones added that he and Rahami enjoyed talking about football and cars, and often met up in a local park to play basketball.

Patron Ryan McCann, 33, told the New York Times that Rahami could often be found behind the counter and loved to regale clients with stories of the Honda Civics he customized for racing.

But the Rahamis changed after a trip to Afghanistan several years ago, Jones and other sources said.

"He was really religious [after the trip]," said Jones. The family had always dressed in secular clothing but returned with a wardrobe of traditional Muslim clothing. Since then, Rahami had become a lot more serious and had lost interest in his hobbies, neighbours told police.

And was radicalised in Pakistan

Rahami travelled to Afghanistan several times, according to law enforcement sources. In 2011, he spent several weeks in Kandahar, Afghanistan, and Quetta, Pakistan, a Taliban stronghold. While there, he married a Pakistani woman in July 2011.

Two years later, he went to Pakistan again in April 2013, this time for about a year. His brother Mohammad, who had earlier fled from the US to Afghanistan after a local altercation in New Jersey, also travelled to Pakistan while Ahmad was there. At the time, Mohammad had posted on Facebook that while in Quetta, in one instance, they had heard seven bomb blasts over 24 hours, CNN quoted a law enforcement investigation report as saying.

Is that where he got his idea for the two bombs in New York and at least five in various places in New Jersey over the last weekend? Investigations are on.