AUSTIN, Texas (AP) — After the first package exploded on an Austin doorstep, police assured the public that there was no wider threat, no signs of terrorism. The idea of a serial bomber striking random strangers never came up.

The March 2 blast killed Anthony Stephan House, a 39-year-old man with a background in finance and an 8-year-old daughter. Investigators didn't rule out that House may have mishandled homemade explosives.

Hours later, in an interrogation room, detectives told one of House's neighbors their main theory: The deadly package was retaliation, maybe from a drug cartel, for a raid days earlier that seized more than $300,000 and 30 pounds of pot. The cartel just got the address wrong.

"They're saying, 'Who's trying to blow you up?' They're trying to do the whole thing, 'Help us help you, because they're not going to miss again,'" said Mark McCrimmon, an Austin attorney who represents the neighbor.

It wouldn't be the last wrong lead in the three-week search that eventually led to Mark Anthony Conditt, an unemployed community college dropout who blew himself up Wednesday as officers closed in.

The manhunt intensified after more explosions in the weeks that followed House's death. By the time the suspect too was dead, his bombs had killed two people, badly wound four others and unnerved the Texas capital.

On Thursday, authorities gave no indication they were any closer to understanding why Conditt did it. Austin Police Chief Brian Manley said the bomber left behind a 25-minute cellphone recording that amounted to a confession but revealed no clear motive.

It's one last mystery in a case that police struggled to crack. More than 500 federal agents swarmed Austin in what Rep. Michael McCaul, chairman of the House Homeland Security Committee, called the nation's largest bombing manhunt since the 2013 Boston Marathon attacks.

The trail to Conditt included many dead ends among more than 500 phoned-in tips. There were theories that didn't pan out and surveillance cameras that failed to record a glimpse of the suspect.

"They got a lot of calls," McCaul said of investigators, "but not a lot of credible leads."

Early miscalculations stoked frustration in the neighborhoods where the second and third bombings went off on March 12.

Because police initially believed House's death was an isolated attack, they did not warn Austin residents about suspicious deliveries before another package killed 17-year-old Draylen Mason and wounded his mother. Mason and House were both black and related to prominent Austin families, which led police to consider whether they were dealing with a hate crime.

"They didn't consider all the alternatives, and it came back to bite us," said Nelson Linder, president of the Austin chapter of the NAACP.

When the third bomb wounded a 75-year-old Hispanic woman, investigators wondered whether it was actually intended for a neighbor, Erica Mason, who has the same last name as the slain teenager.

Erica Mason, who is white, said she told police she had no connection to Draylen Mason's family. Police now think the shared name was just a coincidence.

Even after three bombings, investigators were still unsure whether they were dealing with a single attacker. "We're not calling it a serial bomber," Manley told reporters on March 12.

A week later, they were.

By then, police had urged residents to report any strange packages. The warning flooded 911 operators with more than 1,000 calls.

Six days after Mason's death, authorities increased the pot of reward money to $115,000 and tried a new tactic to draw the bomber out: a news conference that included a direct appeal for him to get in touch. Hours later, another explosion seemed to be his answer.

The fourth blast, triggered by a tripwire attached to a "children at play" sign that Conditt purchased at Home Depot, was the first on the city's more affluent west side. The new location dampened earlier theories about who the bomber was targeting.

After a fifth explosion Monday at a FedEx processing center outside San Antonio, authorities finally got their big break.

Conditt had not been careful to avoid cameras before entering a FedEx store in southwest Austin disguised in a blond wig and gloves, said McCaul, who called it the bomber's "fatal mistake."

Surveillance at the store also captured a license plate linked to Conditt, which in turn gave authorities a cellphone number they could track.

Texas Gov. Greg Abbott said police were able to monitor Conditt and his movements for about 24 hours before his death. The cellphone number tied Conditt to bombing sites around Austin, but McCaul said Conditt had eluded authorities by powering off the phone for long stretches.

By Tuesday night, police began closing in on Conditt's home in suburban Pflugerville. They finally found him early Wednesday at a hotel north of Austin, and officers prepared to move in for an arrest. When the suspect's sport utility vehicle began to drive away, they followed.

Conditt drove into a ditch on the side of the road, and SWAT officers approached, banging on his window. That's when he ended his life by setting off one of his own devices inside the vehicle.

Police found him because he turned his phone back on, McCaul said.

"He turned it on. It pinged, and then the chase ensued," he said.
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By PAUL J. WEBER and RYAN J. FOLEY, Associated Press
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Associated Press Writer Sadie Gurman in Washington contributed to this report.
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Follow Paul J. Weber on Twitter: www.twitter.com/pauljweber.