The suspected serial bomber who terrorised Austin with a string of exploding packages died yesterday after detonating an explosive device in his vehicle as police closed in on him, authorities said.

Austin police and the FBI tracked him to a hotel parking lot in Round Rock, about 30km north of Austin, where they found him inside his vehicle, Interim Austin Police Chief Brian Manley said. Officers wanted to wait for tactical units to arrive before engaging the suspect, but he started to drive away.

Officials investigate near a vehicle, centre, where a suspect in the deadly bombings that terrorised Austin blew himself up as authorities closed in on him. Photo / AP
Officials investigate near a vehicle, centre, where a suspect in the deadly bombings that terrorised Austin blew himself up as authorities closed in on him. Photo / AP

A bizarre rant apparently written by the same person has emerged on a conservative blog, in which a man named Mark Conditt from the same city argues against gay marriage, abortion and sex offender registries.

"If a women does not want a baby, or is incapable of taking care of one, she should not participate in activities that were made for that reason," writes the author in a post on abortion published on the blog, Defining My Stance.

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The writer also states that "homosexuality is not natural" and is like "trying to fit two screws together and to [sic] nuts together", as well as advocating for the death penalty.

The man stopped on the side of the Interstate 35 frontage road, and as Austin SWAT officers approached, he detonated a bomb, knocking one of the officers backward and injuring him, Manley said.

A SWAT officer then fired at the suspect, who died inside the vehicle, the police chief said. It was unclear whether he died from the explosion or from gunfire. Manley said the suspect sustained "significant" injuries from the blast.

The suspected bomber has been identified as Mark Anthony Conditt, according to two officials familiar with the investigation. Police said Conditt was 24, while some public records suggested he was 23.

In announcing Conditt's death, authorities warned that he may have left additional explosives behind and urged residents of Austin and the surrounding communities to remain vigilant after a bombing campaign that has lasted for nearly three weeks.

Austin Police Chief Brian Manley briefs the media yesterday, in Round Rock, Texas. Photo / AP
Austin Police Chief Brian Manley briefs the media yesterday, in Round Rock, Texas. Photo / AP

"We are concerned that there may be other packages that are still out there," said Christopher Combs, special agent in charge of the FBI's San Antonio office.

Still, Austin Mayor Steve Adler said his city is now breathing a sigh of relief after multiple days of terror.

"They are confident that they have someone who has been responsible for these bombs going off," he said on the Today show. "As a community we're just really relieved and just incredibly thankful for this army of law enforcement that has been in our community here for the last week or so."

News of the suspect's death came after investigators spent days struggling to explain the bombs that had detonated in Central Texas since March 2, a series of blasts that killed two people in Austin, injured four others and frightened the region. That tension remained Wednesday, even after police said the suspect was dead.

"We don't know if there are any other bombs out there and if so, how many and where they may be," Texas Governor Greg Abbott said yesterday morning. "Because this individual, either by mail or by placement or whatever the case may be, may have put other bombs out there."

Manley said police believe that the same bomber was responsible for all five explosions - four in Austin and one at a FedEx facility in Schertz, Texas - and authorities were now investigating whether he had any accomplices. What may have motivated the bombings, Manley said, also remained unknown.

"That's the one thing we don't have right now, is a motive behind this," Manley said. "We do not understand what motivated him to do what he did, and that will also be part of the continuing investigation as we try to learn more about him."

Little was immediately known about Conditt in the hours after police said he was killed. Condit attended Austin Community College between 2010 and 2012, but did not graduate, according to the school. A spokeswoman for the school declined to answer questions about Conditt's time there and whether he had any disciplinary issues, saying they were working with the Austin Police Department to offer "any information they need."

Manley said the information leading police to Conditt came together over the past 24 to 36 hours through surveillance videos and witnesses, who provided tips about his vehicle.

Frank de la Fuente, who was staying at a Red Roof Inn on Highway 35, said he heard an explosion at about 3.30am followed by two gunshots.

The explosion, witnesses said, happened next door, outside another hotel.

"He blew himself up down here," Jeremy Lowe said at the Red Roof Inn, pointing in the direction of the WoodSpring Suites. "They shut down the highway and told everybody to not go anywhere."

This undated photo from a Facebook posting shows Mark Anthony Conditt, the suspect in the deadly bombings that terrorised Austin. Photo / AP
This undated photo from a Facebook posting shows Mark Anthony Conditt, the suspect in the deadly bombings that terrorised Austin. Photo / AP

On Tuesday, the investigation into the bombings expanded after a package exploded at the FedEx facility in Schertz. FedEx said the same person who shipped that package had sent a second one, which federal officials located at one of the company's facilities in Austin.

Federal officials and police said this second package "contained an explosive device [that] was disrupted by law enforcement. No injuries were reported." FedEx said it had given investigators "extensive evidence" about those packages as well as the person who shipped them.

Adler, the Austin mayor, said the bomber's use of the FedEx system "was very helpful." Previously, Adler had said that the more bombings that occurred, the more evidence there would be for investigators. "That proved to be the case," he said early Wednesday.

Police called the attacker a "serial bomber" who had been showing increasing sophistication and skill as the bombings continued. This blast in Schertz was the latest sign that whoever was responsible for the explosions was capable of shifting tactics, an unusual trait for such an attacker.

The bomber "is not stupid. He's being diversified in his methods and attacks, and may have done this before somewhere,'' Malcolm Brady, a retired explosives investigator at the Bureau of Alcohol, Tobacco, Firearms and Explosives, said Tuesday. But each new device - and delivery method - offered new potential leads, such as business records, video or other evidence.

The bombings began with three packages placed at people's homes in east Austin, then shifted to a tripwire-enabled device left along a residential street in another part of the city. After that came the pair of packages sent through FedEx - including one that exploded on a conveyor belt - as whoever was responsible apparently turned instead to a delivery company.

While the explosion at the FedEx center sent investigators to a city about 105 km from Austin, Michael Hansen, the Schertz police chief, said investigators were "confident that neither this facility nor any location in the Schertz area was the target."

ATF agents investigate the scene at a FedEx distribution centre where a package exploded on Tuesday. Photo / AP
ATF agents investigate the scene at a FedEx distribution centre where a package exploded on Tuesday. Photo / AP

Instead, the focus remained on Austin, where the previous four explosions had occurred between March 2 and March 18.

The first explosion killed Anthony Stephan House, 39, when it detonated at his home on March 2. Ten days later, another explosion killed Draylen Mason, a college-bound 17-year-old known for his passion for music. That blast also injured Mason's mother.

These explosions prompted speculation that the victims were targeted because of their family connections: House's stepfather, is friends with Mason's grandfather Norman, and both are prominent fixtures at a local black church.

Authorities also said they were considering whether the bombings could be motivated by racial hatred, noting that both House and Mason were black.

Hours after Mason was killed - while police were still responding to that blast - another explosion seriously injured Esperanza Herrera, a 75-year-old woman visiting her elderly mother's house. Investigators believed that package was addressed to someone else and detonated while Herrera was carrying it, according to people familiar with the case.

On Sunday, two more men - both in their early 20s - were injured just hours after police made a plea for the bomber to come forward to speak to authorities. Rather than being left at someone's home, that package was on the side of the road, rigged with a tripwire and anchored to a for-sale sign. When it detonated in an affluent part of southwest Austin, the two men were taken to the hospital with serious injuries.

The package that exploded in Schertz early Tuesday was heading to Austin, police said. Authorities also believed it was sent from a FedEx location in Sunset Valley, an enclave city in Austin.

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

"That bomb was very different from the other three," Manley, the interim police chief, 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, meanwhile, 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 1200 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.

President Trump cheered the fate of the suspect in a tweet early Wednesday, saying, "AUSTIN BOMBING SUSPECT IS DEAD. Great job by law enforcement and all concerned!"