The trip wire that set off the fourth explosion in Austin's horrifying March, authorities now chillingly say, was tied to a "caution, children at play" sign that the accused bomber had bought at a Home Depot.

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But the breaching of that wire and the resultant detonation Sunday, which sent two men to the hospital, also set off an increasingly feverish 55 hours of escalating bombing activity and community quaking that ended only with bombing suspect Mark Conditt's death in yet another blast.

Austin was already reeling after two deaths in three explosions in packages left on doorsteps on March 2 and March 12. A Northeast Austin construction project manager and a promising teenage musician, both part of prominent African-American families in Austin, had been killed, and two others injured by the first wave of bombs. But given the consistent method of those first three bombings, the danger seemed recognizable: Avoid picking up any unexpected package on the porch and perhaps the worst could be avoided.

But the Travis Country bombing on March 18, which was triggered by a trip wire, followed closely by an explosion of a package at a FedEx sorting facility north of San Antonio just over a day later, and then the discovery of another package containing a bomb at a FedEx facility in Southeast Austin, signaled that something more random was happening. The bomber, it now seemed, had everyone in his sights, and any package was now suspect.

And the whole nation was watching.

Common Traits Of A Serial Bomber

By Monday, commentators as diverse as President Donald Trump, University of Texas football coach Tom Herman and Chance the Rapper had weighed in on the run of bombings. Dozens of Texas Rangers and something like 500 agents from the FBI, the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, and the Postal Service had descended on Austin, pouring over physical and electronic evidence with Austin police. Austin and its troubles were now the subject of cut-ins on cable news and prominent coverage in The New York Times and Washington Post.

And officials, given the bomber’s new tactics, began to describe his handiwork as “sophisticated.” But even from the outside, the thought occurred that the increasing pace and morphing form of the attacks in fact could be rash and play into the hands of the bomber’s battalion of pursuers.

So, if Austin writ large seemed to hold its composure in the face of the final two frenzied days, perhaps panic was staved off by this sense that the bomber’s increasing boldness would lead to his capture.

FedEx bombs

After a relatively calm Monday, the fifth explosion came just after midnight Tuesday in an unexpected spot: that FedEx plant a few hundred yards west of Interstate 35 in Schertz. The bomb — sent from a FedEx store in Sunset Valley and intended for delivery to an undisclosed address in Austin — instead detonated on a conveyor belt at the Schertz facility. No one was injured.

Austinites, awaking to this news Tuesday morning and still trying to put it in context, quickly learned that law enforcement had flocked to yet another FedEx facility near Austin-Bergstrom International Airport. They discovered another bomb in a package intended for somewhere in Austin — this one intact — and confiscated what seemed to be another important piece of evidence.

That package too had been sent from the Sunset Valley FedEx shop, officials said.

That meant that virtually any package or backpack — along the road, at work, arriving at a home — was now suspect. At least one delivery service instructed its couriers to knock on doors rather than merely leave a package for recipients to find later. Calls to 911 in Central Texas for “suspicious” packages swelled to over 1,000 cumulatively. And Austin interim Police Chief Brian Manley took time out from the around-the-clock manhunt to brief a skittish Austin City Council about the effort.

Interim Austin Police Chief Brian Manley, right, stands with other members of law enforcement as he briefs the media, Wednesday, March 21, 2018, in the Austin suburb of Round Rock, Texas. The suspect in a spate of bombing attacks that have terrorized Austin over the past month blew himself up with an explosive device as authorities closed in, the police said early Wednesday.

Credit: Eric Gay

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Credit: Eric Gay

Net closing

Perhaps the best illustration of the public's waxing anxiety came Tuesday evening in what at first seemed like the bomber's next strike, at a Goodwill Industries store on Brodie Lane in South Austin. An injured man was rushed to St. David's South Austin Medical Center. Flashing lights and reporters swarmed the area.

But, were all told soon after that what had detonated was an "artillery simulator," a tube-like device used in military exercises that gives off a loud report and a flash of fire when activated. Someone other than Conditt, it appears — whether with dubious judgment or ill intent is not known at this point — had left a box of donated items at Goodwill, officials said, including the dangerous hardware. A worker's hands were burned when the device went off.

What the public could not know at this point was that law enforcement had identified Conditt as the sole suspect behind the run of bombings, and in fact Tuesday evening filed federal criminal charges for unlawful possession and transfer of a destructive device against the 23-year-old Pflugerville man. The net was closing.

Suspected Austin serial bomber, 23-year-old Mark Conditt.

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Credit: undefined

His end, and soon thereafter something like a community-wide release of breath and thankfulness, came somewhere around 2:45 a.m. Wednesday. Police had staked out Conditt, who was parked at a hotel on I-35's west side in Round Rock, and were waiting for S.W.A.T. officers to arrive. But Conditt, perhaps perceiving their presence, pulled out onto the southbound frontage road lane.

But he soon swerved to a stop in the grass median. Moments later, what would be Conditt's seventh known bomb exploded, this one in the cab of his red Nissan Pathfinder.