Technology and luck lead police to backyard hideout

The hunt for the Boston bombing suspects was successful through a combination of technology, public co-operation and sheer luck.

United States media reports have revealed the work that went on behind the scenes, but also the key human tips that allowed the authorities to catch suspect Dzhokhar Tsarnaev, 19, after the death of his brother Tamerlan, 26.

The Washington Post wrote: "It is an object lesson in how hard it is to separate the meaningful from the noise in a world awash with information."

Investigators, the newspaper reported, used a warehouse in Boston's Seaport district to hold the hundreds of pieces of bloodied clothing from the bombing on Tuesday. In half of the room, investigators sifted through hundreds of hours of video, Boston Police Commissioner Edward Davis told the Post. One agent watched the same segment of video 400 times.

They began to focus on two men who brought two backpacks to near the marathon finish line but then left without the bags.

Davis had learned of the importance of video after the London Underground bombings in July 2005, when surveillance cameras led to the identification of suspects.

Davis said he was told facial-recognition software did not identify the two men, even though images of both men are in official databases.

But tips from the public were also key. A victim of the Boston bombing, Jeffrey Bauman, wrote a note: "Bag. Saw the guy, looked right at me."

They had been tracked down as much because of the efforts of a 58-year-old electrical engineer named Bob Leonard who, when the first fuzzy images of the brothers appeared, realised he had clear pictures of their faces at the marathon.

Then there were David Henneberry and his wife Beth. After the city went into lockdown, they were cooped up for about 12 hours. When the curfew was lifted, they looked forward to a breath of fresh air before nightfall.

But as Henneberry, 66, strolled through the back garden of his house in Watertown, he realised something was amiss. The tarpaulin covering his boat was flapping in the wind and the cord that had held it had been severed.

"He got closer and realised that one of the retention straps had literally been cut," explained Robert Duffy, Henneberry's stepson. Henneberry decided to investigate.

"He put his ladder up on the side of the boat and climbed up," said George Pizzuto, a neighbour.

"And then he saw blood on it, and he thought he saw what was a body lying in the boat. So he got out of the boat fast and called police."