ROUND ROCK, United States (NYTIMES) - It was not much - surveillance footage in and near an Austin-area FedEx store showing a man in a disguise dropping off packages. But for investigators from federal, state and local agencies who had been hunting a mysterious and prolific bomb-maker, it was what they needed - their first big break.

Up to that point in a two-week investigation, officials had never laid eyes on the man they believed was responsible for terrorising the Texas capital since March 2. In the security footage, a red 2002 Ford Ranger could be seen, officials said. Because the authorities did not have a license plate number, they began combing through records - all of them, for every vehicle with the same make and model in Texas. Investigators then began trying to match the records with a white male, possibly in his 20s.

And there was another, more unorthodox clue from the surveillance video: The suspect's hands. He was wearing pink construction gloves. Investigators determined the same type of gloves were available at Home Depot, and they began going through hours of surveillance video from Home Depot locations in and around Austin. They got a hit: security video from one store appeared to show the same suspect.

Officials had now whittled down the number of potential licence plates and began tailing a handful of people. One of them turned out to be Mark Conditt - the man that the authorities now believe was the Austin serial bomber.

In a matter of hours, Conditt's bombing spree, as well as his life, would be over.

As SWAT officers closed in, Conditt - a 23-year-old man from the Austin suburbs with no criminal record - ignited one of his homemade devices from inside his vehicle early on Wednesday and killed himself before he could be apprehended. The dramatic and deadly trail of homemade explosions that left two people dead and injured four others ended in a ditch off Interstate 35 in Round Rock, with the windows of his vehicle blown out and his motive as unknown as ever.

In the hours after Conditt's death, a portrait of the bomber, his bombs and his techniques emerged, along with the story of how he was finally stopped - the lucky breaks, investigative ingenuity and technology that helped catch one of the most elusive serial bombers in recent decades.

CONFESSION

By the end of the day on Wednesday, police had another tool: A 25-minute confession, left on the suspect's phone, in which he attempted to describe his odyssey. "It is the outcry of a very challenged young man talking about challenges in his personal life that led him to this point," the Austin police chief, Brian Manley, said.

Interviews with political leaders briefed on the inquiry, along with briefings from investigators and a federal law enforcement source, shed light on an investigation that saw hundreds of federal agents descend on Austin, gathering and reconstructing bomb fragments, interviewing witnesses and gathering video footage. "We haven't seen an effort like this in many, many years," said Christopher Combs, special agent in charge of the FBI's office in San Antonio.

Officials said Conditt planted one bomb in the upscale Travis County neighbourhood of Austin on Sunday, and tied the bomb's tripwire to a "Caution: Children at Play" sign - which he himself put next to the sidewalk and that he bought, along with four others, at Home Depot. Investigators used his cellphone data to put him at the scene of explosions in Austin and also got his Google search history. But officials said the crucial first break came when Conditt mailed the packages at the FedEx store earlier this week.

Conditt's suicide left more questions than answers about who he was, how he became a bomb-maker and why he did it. But Manley seemed to ease worries about more bombs when he said all seven had been accounted for. Law enforcement officials had worried that Conditt might have placed or sent additional bombs in the hours before he died. And officials said they were still looking into whether Conditt had any accomplices.

In the Austin suburb of Pflugerville, where Conditt grew up and lived, a steady fear persisted throughout the day, even after his death. Neighbours were forced to evacuate from the area surrounding the house Conditt shared with two roommates after investigators found explosive materials there. They were allowed to return late in the day.

The Austin police said they had questioned Conditt's two roommates. One had been released; the other was still being questioned as of Wednesday afternoon. Neither roommate was identified. Outside Conditt's parents' home in Pflugerville, Detective David Fugitt with the Austin police said Conditt's family was cooperating and was allowing investigators to search the property, including several backyard sheds.

"We don't have any information to believe that the family had any knowledge of these events," Fugitt said.

'VERY POLITE'

Pflugerville is a tranquil Austin suburb about 30km northeast of downtown. It is a spacious town of 59,000 that has long made its unusual name with the silent first letter part of its charm, as visitors notice when they pass such businesses as Pfast Lube. At times on Wednesday, Conditt's hometown was transformed. Military-style SWAT vehicles sped down the wide avenues. Neighbours and friends said they were stunned that Conditt was the serial bomber.

"He always seemed like he was very polite," said Jeff Reeb, 75, who has lived next door to Conditt's parents for about 17 years. "It's extremely shocking. My summation is it doesn't make any sense. It just doesn't make any sense, which, most of these things like this, don't make any sense." Conditt was a home-schooled student who had attended Austin Community College. He described himself on a blog as "not that politically inclined" but expressed conservative views on issues like same-sex marriage and the death penalty. Friends and neighbours described him as a loner.

"He was a nerd, always reading, devouring books and computers and things like that," said Donna Sebastian Harp, who had known the Conditt family for nearly 18 years. "He was always kind of quiet."

The attacks began when a package bomb detonated on the porch of an Austin home, killing Anthony Stephan House, 39. That was followed 10 days later by two bombs that were found outside homes, one of which killed a 17-year-old boy.

The first three bombs were apparently detonated when they were picked up or jostled. Later, on Sunday, a package bomb exploded in the Travis Country neighbourhood, set off by the tripwire. The fifth explosion occurred at a FedEx centre in Schertz, outside San Antonio on Tuesday. Another bomb, this one unexploded, was found at another FedEx facility in Austin the same day.

"We do not understand what motivated him to do what he did," Manley told reporters.

In a mere 19 days, the bombing sprees sparked fear across the Austin and San Antonio regions of Central Texas, evoking the nowhere-is-safe quality of the anthrax mailings of 2001 and the Washington-area sniper attacks of 2002. For a young man of 23 who did not complete a degree from Austin Community College, his devices and shifting methods as a serial bomber left some of the country's most experienced federal explosives experts baffled early on in the investigation.

And yet, that change in his tactics is largely what led police to him.

His first three bombs were hidden in packages that were not mailed but instead placed on people's doorsteps. His fourth was set off using a tripwire across the Travis Country sidewalk. But his fifth was different - he shipped it from the FedEx store, which captured him on security video, wearing a baseball cap and a black T-shirt and standing at a counter, in addition to other surveillance video from the area. He shipped two package bombs there, and when one of them accidentally exploded at a FedEx centre in Schertz, investigators traced the shipments back to the FedEx store and, ultimately, to him.