The suspect in a spate of bombing attacks in Austin, Texas, that have killed two people and injured four others this month blew himself up with an explosive device as authorities closed in, police have said.
Authorities had zeroed in on the suspect in the last 24 to 36 hours and located his vehicle at a hotel on Interstate 35 in the suburb of Round Rock, Austin police chief Brian Manley said at a news conference.
They were waiting for ballistic vehicles to arrive to move in for an arrest when his vehicle began to drive away, Mr Manley said.
Authorities followed the vehicle, which ran into a ditch on the side of the road, the police chief said.
When members of the Swat team approached, the suspect detonated an explosive device inside the vehicle, the police chief said.
The blast knocked back one officer, while a second officer fired his weapon, Mr Manley said.
Authorities identified the suspect only as a 24-year-old white man and would not say if he was from Austin.
Austin has been targeted by four package bombings since March 2 that killed two people and seriously wounded four others.
A fifth parcel bomb detonated at a FedEx distribution centre near San Antonio early on Tuesday.
Authorities 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.
He said the suspect is believed to be responsible for all the major Austin bombings.
Authorities also said they did not know his motive.
Fred Milanowski, an agent with the US Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), said it was "hard to say" if the bombing suspect was acting alone.
"What we do know is we believe the same person built each one of these devices," said Mr Milanowski, the agent in charge of the Houston division of the ATF.
"We are not 100% convinced there's not other devices out there. We still want the public to be vigilant."
Asked if the suspect built bombs before the Austin attacks, Mr Milanowski said: "We know when he bought some of the components. It's hard to say whether he was building along the way"
Austin mayor Steve Adler thanked law enforcement for their work in bringing down the suspect and urged residents to continue to report anything that appeared suspicious or out of place.
"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," he said.
Isaac Figueroa, 26, said he and his brother heard sirens and helicopters early on Wednesday and drove towards them, then cut through nearby woods on foot after they hit a police roadblock.
Mr Figueroa said they saw a silver or grey Jeep Cherokee that was pinned between black and white vehicles and "looked like it had been rammed off the road".
He said he saw police deploy a robot to go to examine the Jeep.
President Donald Trump, who had earlier said whoever was responsible for the Austin bombings was "obviously a very sick individual or individuals", tweeted, "AUSTIN BOMBING SUSPECT IS DEAD. Great job by law enforcement and all concerned!"
The suspect's death followed a day of rapid-fire developments in the case.
On Tuesday, a bomb inside a package exploded at around 1am local time as it passed along a conveyor belt at a FedEx shipping centre in Schertz, north east of San Antonio and about 60 miles south west of Austin.
One worker reported ringing in her ears and was treated at the scene.
Later in the morning, police sent a bomb squad to a FedEx facility outside the Austin airport to check on a suspicious package.
Federal agencies and police later said the package had contained an explosive that was successfully intercepted and that it too was tied to the other bombings.
Authorities also closed off an Austin-area FedEx store where they believe the bomb that exploded in Schertz was shipped.
The Schertz blast came two days after a bombing wounded two men on Sunday night in a quiet Austin neighbourhood about three miles from the FedEx store.
It was triggered by a nearly invisible tripwire, suggesting a "higher level of sophistication" than agents saw in three package bombs previously left on doorsteps, Mr Milanowski said.
Authorities have not identified the two men who were hurt on Sunday, saying only that they are in their 20s.
But William Grote told the Associated Press that his grandson was one of them and that he had what appeared to be nails embedded in his knees.