AUSTIN (CBSDFW.COM/AP) — First packages with bombs inside began appearing on the porches of residents in Austin, then a wire triggered an explosion near a street, now this morning a package bomb has exploded inside a FedEx distribution center near San Antonio.

schertz fedex 1 Bomb Carnage Across Texas Now Random; Arrest Doesnt Appear Close

The scene outside a FedEx distribution center in Schertz, Texas, where a package bomb exploded on March 20, 2018 (credit: Jason Allen/CBS 11 News)

William Grote says the attack by a suspected serial bomber that has terrorized Austin for weeks left what appeared to be nails embedded in his grandson’s knees on Sunday night.

Police and federal agents had said that the blast triggered along a street by a nearly invisible tripwire suggested a “higher level of sophistication” than they had seen in the three earlier package bombs left on doorsteps, and meant the carnage was now random, rather than targeted at someone in particular. That idea has perhaps been further supported after the FexEd bombing Tuesday.

Two people are dead and now five have been injured, and authorities don’t appear closer to making any arrests in the bombings that have rocked the capital city.

Authorities haven’t identified the victim at the FedEx plant or the person injured by the tripwire explosion, but Grote told The Associated Press that his grandson was one of the two men wounded in southwest Austin’s quiet Travis Country neighborhood. They suffered what police said were significant injuries and remained hospitalized in stable condition.

Grote said his grandson is cognizant but still in a lot of pain. He said the night of the bombing, one of the victims was riding a bike in the street and the other was on a sidewalk 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.”

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,” Grote said.

That was a departure from the earlier bombings, which at the time only 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-neighbor 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.

“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. He would not elaborate, though, saying he didn’t want to undermine the investigation.

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, the tripwire blast was west of the highway and the FedEx package explosion was in Schertz, about 20 miles northeast of San Antonio. 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.

Thad Holt, 76, said he is now watching his steps as he makes his way through a section of town near the tripwire attack. “I think everybody can now say, ‘Oh, that’s like my neighborhood,'” he said.

Fred Milanowski, agent in charge of the Houston division of the Federal Bureau of Alcohol, Tobacco, Firearms and Explosives, said the tripwire bomb was anchored to a metal yard sign near the head of a hiking trail.

“It was a thin wire or filament, kind of like fishing line,” he said. “It would have been very difficult for someone to see.”

Before the FedEx explosion, Milanowski said authorities had checked more than 500 leads. During a press conference Monday police asked anyone with surveillance cameras at their homes to come forward with the footage on the chance it captured suspicious vehicles or people.

Noel Holmes, whose house is about a mile away, was stunned by how loud Sunday’s explosion was.

“It sounded like a very nearby cannon,” Holmes said. “We went out and heard all the sirens, but it was eerie. You didn’t feel like you should be outside at all.”

The PGA’s Dell Technologies Match Play tournament is scheduled to begin in Austin on Wednesday, and dozens of the world’s top golfers were to begin arriving.

“I’m pretty sure the tour has enough security to keep things safe in here. But this is scary what’s happening,” said golfer Jhonattan Vegas, already in town.

A few hours after the bomb explosion in Schertz, police sent a hazardous materials team to a FedEx facility in Austin to check on a suspicious package there. There was no immediate word about whether that package contained a bomb.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)

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