SCHERTZ, Texas — The latest in a wave of bombings rattling Central Texas brought a widening investigation to this city outside San Antonio on Tuesday, after an explosion at a FedEx facility signaled that whoever is responsible for the attacks had offered police potentially critical new clues while again shifting tactics.

The blast early Tuesday – the fifth since March 2 – came as investigators struggled to explain the bombing campaign that began with a series of packages placed at people’s doorsteps in east Austin, escalated to a tripwire-enabled device left along a residential street and, on Tuesday, shifted to an explosive device shipped through a delivery company.

The same person who shipped that explosive sent another package that was intercepted before delivery and was turned over to the FBI, according to FedEx. Federal officials confirmed that package also contained an explosive device.

Police have described the unknown attacker as a “serial bomber” who has been showing increasing sophistication and skill. The two explosions on Sunday and early Tuesday also suggested a worrisome – and unusual – willingness to change gears.

The bomb in Schertz exploded just after midnight while being carried on an automated conveyor belt at a FedEx center about an hour south of Austin, the city that has been the focus of the blasts. One employee at the center said it caused ringing in her ears, but no one else was wounded, police said.

The package was en route to Austin, according to police, and officials said they think it was the work of the same person or people responsible for the four earlier explosions in the Texas capital. Michael Hansen, the Schertz police chief, said investigators are “confident that neither this facility nor any location in the Schertz area was the target.”

FedEx also said Tuesday that by using the delivery service, the person who shipped the packages left “extensive evidence,” which the company turned over to investigators.

“We have also confirmed that the individual responsible also shipped a second package that has now been secured and turned over to law enforcement,” FedEx said in a statement. “We are thankful that there were no serious injuries from this criminal activity. We have provided law enforcement responsible for this investigation extensive evidence related to these packages and the individual that shipped them collected from our advanced technology security systems.”

In a statement Tuesday evening, the Austin police, the FBI and the ATF confirmed that the package found in Austin that morning “contained an explosive device [that] was disrupted by law enforcement. No injuries were reported.”

As tension lingered in Austin, authorities raced Tuesday night to a reported explosion in the city’s southwest area where a man in his 30s was believed to be injured. But police said later it appeared this was an incendiary device, not an explosive, and appeared unconnected to the previous explosions.

Meanwhile, investigators were carefully examining the unexploded FedEx package, hoping it could provide new evidence pointing to a possible suspect.

The discovery of an unexploded device linked to the case could prove crucial because it could lead to the identity of a suspect or suspects; the materials used to assemble a bomb can be traced back to a supplier – and, in many cases, the individual purchaser.

The suspect “is not stupid. He’s being diversified in his methods and attacks, and may have done this before somewhere,” said Malcolm Brady, a retired AFT explosives investigator. But each new device – and delivery method – offers new potential leads, such as business records, video or other evidence.

“It’s a big jigsaw puzzle, and you put all the pieces of information together and go from there,” he said.

Investigators on Tuesday also searched a FedEx facility in Austin – where the package that detonated in Schertz probably would have been sent next – looking for other package bombs there, according to one person familiar with the investigation.

Brian Manley, the interim Austin police chief, said his department had sent officers to Schertz to help investigate the “new development” there.

“The working theory right now . . . is that that was a package that was in the shipping center destined for Austin,” he told the Austin City Council on Tuesday morning. All four explosions in Austin have occurred outside the city’s core, which includes downtown, the Texas Capitol and the University of Texas.

San Antonio Police Chief McManus had said, during a morning news briefing, that officials believed a second package found at the Schertz facility was “also loaded with an explosive device that they are working on right now.” A spokesman later issued a statement saying: “There is no secondary device at the Schertz facility.”

Finally, officials confirmed late Tuesday that a second package found in Austin had contained an undetonated bomb.

The confusion and contradictory statements underscored the frantic pace of the investigation, which now includes more than 300 federal agents along with scores of local law enforcement officers in Texas.

President Donald Trump said Tuesday that the federal government is working “hand in hand” with local authorities to “get to the bottom” of the bombings in Austin and find those responsible.

The package that detonated early Tuesday is believed to have been sent from a FedEx location in Sunset Valley, an enclave city within Austin, police said.

“The FBI believes that the package that detonated in Schertz may have originated from here,” said Sunset Valley police Lt. Rich Andreucci.

The police department cordoned off the FedEx storefront – located three miles from the site where a bomb, rigged with a tripwire, detonated Sunday night – but neighboring stores in the shopping center were open.

“The more we’re sitting here, the more we realize it’s serious,” said Jessica Wilkinson, who was celebrating her 37th birthday by having lunch outside with her sister and mother. “It’s just all over the place.”

A mother of two children, ages 8 and 4, Wilkinson said it’s been a scary time to live in Austin, “but it’s so random, it’s hard to change anything in my day-to-day life to avoid it.”

Her mother, Kellie Metzler, 59, said she thought about texting Wilkinson to say, “Don’t be scared; I sent a couple of packages for your birthday.” Metzler said she was infuriated by the seeming randomness of the bomber’s targets.

“Why pick on people you don’t even know?” Kellie Metzler said. “Not one of them did a thing to you. I just don’t get that.”

The first three bombs – one on March 2 and a pair that detonated March 12 – were in packages dropped off at people’s homes, authorities said. The fourth bomb was placed on the side of the road in a residential neighborhood and was rigged with a tripwire; when it detonated Sunday night, two men were wounded.

The first three explosives all detonated in eastern Austin, affecting areas where black and Hispanic residents live, leading to suggestions that the attacks might have been motivated by racial bias. The explosion Sunday night detonated in an affluent, predominantly white neighborhood and injured two white men in their 20s.

Police and experts have pointed to the change in tactics as suggesting the proficiency of whoever is responsible.

“That bomb was very different from the other three,” Manley told the City Council. “The first three appeared to be targeting a specific residence, resident address. And whether they were targeting the person at that address or not, we know they were placed on a specific doorstep at a specific home.”

The device Sunday night, by contrast, was seemingly intended to detonate at random, ratcheting up the fear in a city already unnerved by the package explosions.

Police said Tuesday morning that they had received more than 1,200 calls about suspicious packages since March 12, the day two bombs detonated; one-third of the calls came in between Monday morning and Tuesday morning.

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