“Second, very importantly, we need to go throughout the day to make sure that we rule out whether there was anybody else involved in this process,” Mr. Abbott said.
Law enforcement authorities swept into Mr. Conditt’s hometown of nearby Pflugerville and spent hours closeted with his parents in their white clapboard home with an American flag hanging outside.
“We do not understand what motivated him to do what he did,” the Austin police chief, Brian Manley, told reporters.
Mr. Conditt was a quiet, “nerdy” young man who came from a “tight-knit, godly family,” said Donna Sebastian Harp, who had known the family for nearly 18 years.
He was the oldest of four children who had all been home-schooled by their mother, Ms. Harp said, but he had also attended Austin Community College.
“He was always kind of quiet,” she said. “He was a nerd, always reading, devouring books and computers and things like that.”
“There was no violent-type activity,” Ms. Harp said. “He was always gentle and quiet.”
In announcing the arrest, Chief Manley said the authorities were still trying to determine whether there were accomplices.
The police spent hours inside the home of Mr. Conditt’s parents. Detective David Fugitt with the Austin police said the family was cooperating and was allowing investigators to search the property, including several backyard sheds.
No explosives had been found so far, Mr. Fugitt said, though police planned to bring in a bomb-sniffing dog as a precaution.
“We’re going to run the dog through the house, as well as the buildings on the back side of the residence,” he said.
The authorities said the family would be releasing a statement later.
“They wanted to express their condolences to the families of those who’ve been affected, and that will be reflected in the statement,” Mr. Fugitt said. “This family has been very cooperative. They’ve gone above and beyond, to answer any questions that we’ve had. We don’t have any information to believe that the family had any knowledge of these events.”
Of the family, he added: “They’re having a difficult time. This is certainly a shock to the conscience.”
The blocks surrounding the suspect’s home remained cordoned off.
Real estate records show that Mr. Conditt and his father, William Conditt, bought a house together in Pflugerville in 2017, and family friends said the younger Mr. Conditt was remodeling it.
But neighbors said they saw little of him.
“I think he was pretty much a loner,” said Jay Schulze, a network engineer who lived about two blocks down, adding that Mr. Conditt spent most of his time with his parents.
Another neighbor, Jeff Reeb, 75, said the Conditts had never expressed concerns about their son to him.
“I can tell you nothing about him personally, except that he was a nice, young kid,” Mr. Reeb said. “He always seemed like he was smart. And he always seemed like he was very polite.”
Mr. Reeb added: “My summation is it doesn’t make any sense.”
Austin has been in the grip of the wave of attacks since March 2.
Gary L. Bledsoe, the president of the Texas N.A.A.C.P. and an Austin-based lawyer, said on Wednesday, “It is a serious relief to all of us in the Austin community, but we still need to beware of trip bombs and even mailed packages based upon recent events.”
The first explosions hit African-American residents whose families are well-known in the city’s black community, though two white men were injured by an explosive triggered by a tripwire on Sunday.
The suspect is believed to be responsible for at least six bombs that killed at least two people and wounded five. Four bombs detonated in various locations in Austin where they had been left. Another detonated at a FedEx distribution center in Schertz, Tex., near San Antonio, and a sixth was found, unexploded, in a FedEx facility near Austin’s airport.
The attacks began when a package bomb detonated on the porch of an Austin home, killing Anthony Stephan House, 39. That was followed 10 days later by two bombs that were found outside homes, one of which killed a 17-year-old man.
The first three bombs were apparently detonated when they were picked up or jostled. Later, a package bomb exploded outside another Austin home, set off by a tripwire. The bombs at the FedEx centers were found on Tuesday.
“Within the past 24 to 36 hours, we started getting information on one person of interest,” Chief Manley said. “This person of interest ultimately moved to being a suspect.”
The suspect’s vehicle was traced to a hotel in Round Rock, just north of Austin, Chief Manley said, where a SWAT team surreptitiously surrounded the hotel and called other specialized units. But the suspect drove away before those teams could arrive.
Officers followed the suspect, who stopped in a ditch off Interstate 35, and SWAT officers approached the vehicle on foot.
“The suspect detonated a bomb inside of the vehicle, knocking one officer back” and slightly injuring him, the police chief said. Another officer fired his gun at the vehicle.
Michael Luna, a guest at a Red Roof Inn near the confrontation, told a local news channel that he heard the explosion from the bomb, which sounded as if it had gone off 100 to 200 yards away, when he was smoking a cigarette in the parking lot. Mr. Luna, who said he had been in the military, said that the explosion sounded like two grenades going off at the same time, and that he heard a pop afterward that might have been gunfire.
The section of Interstate 35 near that confrontation was a traffic nightmare for hours as commuters moved at a glacial pace in the southbound lanes, many of them presumably unaware of what had happened. State troopers barred access at several ramps along that stretch of the highway.
By Wednesday morning, aerial video footage of the area from KVUE, a local television affiliate, showed a red sport utility vehicle with blown-out windows next to a blue tarp, surrounded by investigators’ vehicles.
Reports of suspicious packages continued to send ripples of worry around the area. In the late morning, the Austin police said on Twitter that they temporarily evacuated a building at an address that appeared to be a FedEx facility, adding that the scene was secure.
Mayor Steve Adler of Austin said that the city’s residents should continue to watch out for suspicious packages that the bomber may have planted before his death. He expressed hope that residents who had been brought closer together during the attacks would continue to watch out for each other as the threat receded.