The Baileys convened a family meeting Tuesday over breakfast. This was an attempt to answer impossible questions from their four children, and, perhaps most important, impart advice the couple never believed they would have to give.

“If you see anything, anything at all, you tell your mother and me,” Steve Bailey, an oil and gas executive, told the kids.

Two evenings earlier, a bomb exploded a block away, along the route the children walk each day to and from the nearby Regents School of Austin, a private Christian school many kids from the well-to-do neighborhood attend. If a pair of mountain bikers had not tripped the wire setting off the bomb, which was tucked in a box filled with nails, the device might still have been lurking as the neighborhood kids made their way to Monday morning classes.

“Of all the neighborhoods in Austin?” Bailey asked. “But I guess everyone in this town is asking the exact same question.”

For 18 days, this city of music and technology, education and pioneering cuisine has lived the kind of anxious life that more commonly defines the daily routine in distant, troubled countries. A serial bomber, motive unknown, has moved in a clockwise sweep around the city, from northeast to southwest, with sophisticated devices blowing up on doorsteps and a bike path.

Police tape hangs in the neighborhood where a bomb went off in Austin on Sunday night, the fourth attack connected to what police are calling a “serial bomber.” (Carolyn Van Houten/The Washington Post)

The morning began here Tuesday with bomb squads called to a vast FedEx facility near the airport where a “suspicious package” — a phrase that has haunted this city since March 2 — was discovered. Police opened trucks and warehouse bay doors, examining packages for much of the morning.

Just a few hours earlier, a package bomb exploded at a FedEx center in Schertz, Tex., about 60 miles south of here. The package apparently was sent from a FedEx mailing office in north Austin and was addressed to someone in the city.

In a statement released Tuesday about the explosion in Schertz, FedEx said it had “confirmed that the individual responsible also shipped a second package that has now been secured and turned over to law enforcement.” An unexploded device could provide investigators with a trove of evidence.

Deflated balloons sway in the wind in the yard of the house where the second Austin bomb killed 17-year-old Draylen Mason. (Carolyn Van Houten/The Washington Post)

Austin is going about its business, but in a cloud of uncertainty and fear as unfamiliar here as spring snow. Austin police have received more than 1,250 calls reporting suspicious packages in the past eight days. Recorded messages ring home phones with warnings of potential suspects in the area.

A columnist for the Austin American-Statesman on Tuesday compared the feeling in the city to the terror that gripped the greater Washington area in October 2002, when a pair of snipers randomly targeted residents for three weeks.

“I had a feeling at those moments that anything could happen,” wrote Ben Wear, who lived in Bethesda, Md., at the time. “I found myself pondering the reality of soldiers in combat, of what it meant to know that at any time some unseen person could point a gun at you and pull the trigger.”

The same rethinking of the world around them is happening here among Austin residents, some of whom said their lives would forever change in small ways to accommodate the new reality. The bomber is using Austin’s particular vulnerabilities, its quirks and characteristics, to carry out a campaign that so far has stymied investigators.

Austin residents love their home-delivery services, such as Amazon and Instacart, a grocery chain that provides store-to-doorstep service. Residents can in some cases expect their orders within hours, and on most days, UPS and FedEx trucks are a common feature of the city streetscape.

The first two bombs were delivered to doorsteps, including an early-morning package for 1112 Haverford Dr., where Anthony Stephan House lived, next to a home where two tiny bikes with training wheels were parked outside Tuesday morning.

The explosion, which blew out the front door and much of the entryway, sounded like a construction accident to Christin Hume, a photographer who was playing in the backyard with her two dogs at the time of the blast. Both immediately ran inside.

“We bought in this neighborhood because it was safe and quiet,” said Hume, who is 25 and lives five doors down from the bomb site with her husband, Chris, a software engineer.

The neighborhood east of Interstate 35 has changed demographically in recent years with young whites, Latinos and South Asians joining a once solidly African American community. The houses are small and well kept, many of them announcing that home- ­security systems are watching.

“Protected by Pit Bull Security Force,” reads one sign.

Hume said she did not know her neighbors well until that morning, when she opened her house to all those roped-off from the scene. As she spoke Tuesday, a FedEx truck pulled up in front of her house. The driver jumped out with a ­medium-size box — a dog bed Hume had ordered online despite the recent attacks.

“My hope is that this is something that forces people to be friends with their neighbors,” she said. “We all need to know now who is around and who we can go to.”

Investigators have said one ­theory is that the attack on House was racially motivated. At the end of Haverford Drive, Chrystal Murray, an African American 34-year-old payroll analyst with Apple, said she immediately had a similar thought.

Chrystal Murray stands for a portrait outside her family’s home, which is down the street from where the first bomb went off on March 2, in Austin, killing Anthony Stephan House. (Carolyn Van Houten/The Washington Post)

She lives in the home with her mother, who heard the early-morning blast. Murray said of learning that the explosion had killed an African American up the street: “Race was then — and always is — a concern of mine.” She and her neighbors have organized a watch program since the attack.

“There’s just so much hate right now,” Murray said, tracing the increase to the political climate since the 2016 presidential election. “But I guess that has been ruled out now. I just can’t believe people do stuff like this.”

To the south, a different neighborhood, wealthier and whiter, is confronting the same questions and concerns.

Live oaks line the grassy median at the entrance of The Retreat at Travis Country, where playground equipment appears in almost every back yard and American flags hang from almost every portico. Yard signs announce the high school athletes who live inside: “Regents Baseball, John Luke.”

Darkness had just fallen when two white men in their 20s rode their mountain bikes out of Gaines Creek Neighborhood Park, crossing Republic of Texas Boulevard and stopping to walk on Dawn Song Lane.

A box sat between the path and the sidewalk on a grassy strip. Invisible to the two men, a trip line joined the box to a yard sign, apparently stolen from another location in the neighborhood.

The bomb exploded, spraying nails across a broad area. Blood stains the sidewalk, and a basketball-size bald patch on the grass marks out the contours of the bomb. The two men were in good condition and recovering at St. David’s South Austin Medical Center.

Steve Bailey was out of the country when the bomb went off, traveling in Europe and Israel with his son, a high school junior. He heard about the attack in a text from his wife, Angela, who he said was direct with the kids at home about what had happened along the route they walk to school each morning along Eagle Feather Drive to Dawn Song Road.

The family and its neighbors have been wondering: Was the bomb actually meant for the children?

“You have to question everything you do and have done until now,” Bailey said. “We told our kids that this is the sin of man, just like we all possess, only it’s taken to the extreme. You have to have the confidence that our father in heaven has this in hand.”

The streets here are quiet, the chairs set out in many front yards empty. Coco Tapia, a neighbor of Bailey’s, emerged with her dog Buddy for a morning walk. But she was alarmed by a recorded call she had just received, telling her to be on the lookout for a “lean man with blue eyes” seen in the area. She didn’t know what to make of it.

“I’m a little insecure about all of this,” she told Bailey.

Up the street, a woman unloaded groceries from the back of an SUV with her teenage children. She sometimes shops via Insta­cart, but she did the chore herself Tuesday after the attacks; this way, there would be no boxes arriving at her home. She declined to give her name, citing fear about her children’s safety.

A U.S. postal worker nearby filled a cluster of mailboxes with letters and packages. He worked quickly, ear buds in place. Asked if the recent package bombs made him hesitate in his job, he smiled.

“I did three tours in Iraq, so I’m not really afraid of this,” he said, declining to give his name because he did not have permission to speak to the media. “Besides, the job has to get done.”