A package bomb has exploded inside a FedEx distribution centre in Texas as the hunt for a suspected serial bomber continues.
The explosion happened at a facility in Schertz, just north-east of San Antonio, at around 1am local time, FBI special agent Michelle Lee told The Washington Post.
ATF spokeswoman Nicole Strong said that early indications are that no-one was injured.
The blast follows a Sunday night explosion that was triggered on a street by a nearly invisible tripwire, suggesting a “higher level of sophistication” than agents saw in three early package bombs left on doorsteps.
It means the carnage by a suspected serial bomber who has terrorised Austin for weeks is now random, rather than targeted at someone in particular.
William Grote said Sunday’s attack left what appeared to be nails embedded in his grandson’s knees.
Two people are dead and four injured and authorities do not appear closer to making any arrests over the five bombings.
Authorities have not identified Sunday night’s victims, but Mr Grote told the Associated Press that his grandson was one of the two men wounded in south-west Austin’s quiet Travis Country neighbourhood.
They suffered what police said were significant injuries and remain in hospital in a stable condition.
Mr Grote said his grandson is conscious but still in a lot of pain.
He said that on the night of the bombing, one of the victims was riding a bike in the street and the other was on a pavement when they crossed a trapwire that he said knocked “them both off their feet”.
“It was so dark they couldn’t tell and they tripped,” he said. “They didn’t see it. It was a wire. And it blew up.”
Mr Grote said his son, who lives about 100 yards away from the blast, heard the explosion and raced outside.
“Both of them were kind of bleeding profusely,” Mr Grote said.
That was a departure from the three earlier bombings, which involved parcels left on doorsteps that detonated when moved or opened.
The tripwire twist heightened the fear around Austin, a town famous for its cool, hipster attitude.
“It’s creepy,” said Erin Mays, 33. “I’m not a scared person, but this feels very next-door-neighbour kind of stuff.”
Authorities repeated prior warnings about not touching unexpected packages and also issued new ones to be wary of any stray object left in public, especially one with wires protruding.
“We’re very concerned that with tripwires, a child could be walking down a sidewalk and hit something,” Christopher Combs, FBI agent in charge of the bureau’s San Antonio division, said in an interview.
Police originally pointed to possible hate crimes, but the victims have now been black, Hispanic and white and from different parts of the increasingly diverse city.
Domestic terrorism is among the variety of possible motives investigators are looking at.
Local and state police and hundreds of federal agents are investigating, and the reward for information leading to an arrest has climbed to 115,000 dollars (£82,000).
“We are clearly dealing with what we believe to be a serial bomber at this point,” Austin police chief Brian Manley said, citing similarities among the four bombs.
While the first three bombings all occurred east of Interstate 35, a section of town that tends to be more heavily minority and less affluent, Sunday’s was west of the motorway.
The differences in where the blasts have occurred, the lack of a motive and other unknowns make it harder to draw conclusions about a possible pattern, further unnerving a city on edge.
Fred Milanowski, agent in charge of the Houston division of the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, said authorities have checked more than 500 leads.