Police in Texas say they have removed explosives from the home of a man believed to be behind a string of parcel bombs in Austin.
23-year-old Mark Anthony Conditt blew himself up in his car as officers closed in.
Six blasts have killed two people and seriously injured four others.
Fred Milanowski from the Alcohol, Tobacco, Firearms and Explosives Bureau says it may not be over yet:
Mr Milanowski said: "We are concerned that there still may be other devices out there, we want to make sure that if people see suspicious packages or bags that they continue to call 911 and report it to the police "
APD, local, state and federal partners provide update on Austin package bomb murder investigation. https://t.co/5w8F6lmijS— Austin Police Department (@Austin_Police) March 21, 2018
Officers have also warned residents in Austin to remain vigilant in case the suspected bomber whose deadly explosives terrorised the city for three weeks planted more bombs before his death.
Mark Anthony Conditt, an unemployed college dropout who bought bomb-making materials at Home Depot, was tracked down using store surveillance video, mobile phone signals and witness accounts of a customer shipping packages in a disguise that included a blonde wig and gloves. His motive remained a mystery.
Police finally found the 23-year-old early on Wednesday at a hotel in a suburb north of Austin.
Officers prepared to move in for an arrest, and when the suspect's SUV 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.
Within seconds, the suspect had detonated a bomb inside his vehicle, blasting the officers backward, Austin police chief Brian Manley said.
One officer then fired his weapon at Conditt, the chief said. The medical examiner has not finalised the cause of death, but the bomb caused "significant" injuries, he said.
Police discovered a 25-minute video recording on a mobile phone found with Conditt, which Mr Manley said he considered a "confession" to the bombings. It described in great detail the differences among the bombs, he said, but no motive.
"It is the outcry of a very challenged young man talking about challenges in his own life," he added.
Law enforcement officials did not immediately say whether Conditt acted alone in the five bombings in the Texas capital and suburban San Antonio that killed two people and badly wounded four others.
Fred Milanowski, of the US Bureau of Alcohol, Tobacco, Firearms and Explosives, said investigators were confident that "the same person built each one of these devices".
Investigators released few details about Conditt, except his age and that he was white. Neighbours say he was home-schooled.
He later attended Austin Community College from 2010 to 2012, according to a college spokeswoman, but he did not graduate.
Conditt's family released a statement saying they had "no idea of the darkness that Mark must have been in". His uncle, Mike Courtney, said his nephew was a "computer geek" who was intelligent and kind.
Austin was hit with four bombings starting on March 2. The first explosions were from packages left on doorsteps. Then a bomb with a tripwire was placed near a public trail. A fifth parcel bomb detonated early on Tuesday at a FedEx distribution centre near San Antonio.
Police warned of the possibility that more bombs had yet to be found.
"We don't know where this suspect has spent his last 24 hours, and therefore we still need to remain vigilant to ensure that no other packages or devices have been left to the community," Mr Manley said.
By late afternoon, federal officials had a "reasonable level of certainty" that there were no more package bombs "out in the public," said Mr Milanowski, the agent in charge of the Houston division of the ATF. But authorities urged continued awareness just in case.
"We think we're on top of this, but we just don't know," FBI agent Chris Combs said.