ROUND ROCK, Tex. — 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 terrorizing 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.