PFLUGERVILLE, Texas — He worked with his dad around their modest yellow house on Second Street, fixing up a newly purchased home in an old-fashioned, close-knit neighborhood — the kind of place where residents check in on one another.

Mark Anthony Conditt seemed to fit in. Having been home-schooled, the 23-year-old was close to his family, including his sisters. As he neared graduation, he took a government course at Austin Community College and described himself on a class blog as conservative but “not that politically inclined.”

People who knew him say Conditt was quiet and shy.

“Everyone has questions, and everyone wants answers, and we are just shocked,” said grandmother Mary Conditt, who lives in Denver. “This is not the Mark that I know or the grandson that I know. I don’t know who this person was that did all of this.”

But Mark Conditt’s violent plans were revealed, police say, in a string of bombings that terrorized Austin this month.

Cornered by police Wednesday, Mark Conditt detonated explosives inside his car before dawn and ended a bombing campaign that killed two, injured several others and injected anxiety into a city renowned for its creativity and cool.

The terror began with devices left at people’s homes on March 2 and March 12, then moved to an explosive rigged with a tripwire that injured two men this week and two explosives shipped through FedEx.

Interim Austin police Chief Brian Manley said police thought Conditt was connected to all of the explosions, which they first linked to him through his cellphone, according to Texas Gov. Greg Abbott.

Abbot said authorities tracked his movements while “he was little more than a suspect.”

Police found Conditt at a hotel north of Austin and followed him as he drove away and eventually veered off the road. His red SUV was the same vehicle that had been seen at locations linked to the explosions.

As officers neared Conditt’s vehicle, he detonated a bomb that knocked back one of the approaching Austin SWAT officers.

Another officer fired his gun at Conditt, who suffered “significant injuries from (the) blast,” Manley said.

It was not clear whether Conditt was killed by the explosives or the gunfire.

Police said Wednesday evening that Conditt seemed motivated by frustration with his life.

Manley described a 25-minute recording on Conditt’s phone as “the outcry of a very challenged young man talking about challenges in his personal life that led him to this point.”

Mary Conditt, 83, said she last saw her grandson in December when he traveled with his family to her house for Christmas.

Conditt described him as having strong conservative political beliefs but said he wasn’t reactionary and spent time researching political viewpoints before he took a stand.

Mark Conditt recently moved into a house that he and his father had renovated. He invited two roommates to live with him, Mary Conditt said.

“We are, of course, grieving, broken and disappointed,” Conditt said.

What police focused on — and were assisted with by Conditt when he walked into a FedEx office and was caught on camera — was Austin’s affinity for online and other home-delivery services that made front-porch packages something no one would think twice about.

It suggested someone with a knowledge of the city and its habits.

“You just don’t know,” said Rey Casanova, a 42-year-old real estate agent in Pflugerville who said he and his wife buy “everything” online but haven’t for the past two weeks. “You don’t know what’s going to come in the mail.”

But none of this explains why Conditt, who attended a Christian church, veered toward violence, how he made bombs law-enforcement officials described as sophisticated, or why he decided Austin and its residents should be a target.

The FedEx shipments offered a significant moment because investigators were able to obtain surveillance footage of Conditt walking into the FedEx store wearing a wig and gloves, Abbott said.

The public profile he left comprises a series of writings on his political views, socially conservative but far from radical. He opposed abortion and same-sex marriage; he lived on the periphery of a Texas city known as a liberal island in a largely red state. But no evidence so far has emerged of radicalization.