Four bombs have been detonated in Austin, Texas, over the past month including one on Sunday, which left two people wounded.
The first three attacks were parcel bombs left on victims’ front porches whereas police said Monday that the latest was an invisible tripwire.
Here is what we know about the Austin bombings:
No. 1: The first bombing took place on March 2. Anthony Stephan House died when a bomb detonated on his front porch. He was a 39-year-old black man. The bomb tore a hole in the home entrance wall and damaged the front door.
No. 2: The second bombing occurred on March 12. Draylen Mason was killed when a package exploded in his kitchen that morning. The 17-year-old’s mother was also injured in the attack. They were also African-Americans.
No. 3: The third bombing occurred just hours after the first one on March 12. A 75-year-old Hispanic woman was left injured by the explosion.
No. 4: Two men were out for a walk when police say they may have crossed a tripwire, creating an explosion. Officials said both men were white.
In the first three bombings, cardboard packages were delivered to the front doorstep of the house in the middle of the night. Victims opened the packages on their front porches.
In the last bombing, a thin translucent tripwire like fishing line was placed near a hiking trail.
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Police said it was a more advanced design than the previous bombs.
Those differences made it harder to draw conclusions about a possible pattern, further unnerving a city on edge.
Two of the victims can be linked, the Washington Post reports. Mason’s grandfather and House’s stepfather were fraternity brothers and are good friends.
Police are unaware of any motive but have reached out to speak with the aggressor.
“We are clearly dealing with what we expect to be a serial bomber at this point,” Austin Police Chief Brian Manley told a news conference near the site of Sunday’s bombing.
Manley has said the bombings were being investigated as possible hate crimes, but cautioned that Sunday’s attack did not appear to have targeted specific people, and both victims were white.
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Randall Rogan, a Wake Forest University professor is an expert on forensic linguistic analysis who worked with the FBI on the Unabomber case.
He said as time passes, it’s likely the person or people behind the explosions will seek more than just the thrill of the crimes themselves and will desire more recognition, something that could drive them to make contact with police or release some sort of communique or manifesto. He said the new complexity of the fourth bombing might suggest it was a test for something even bigger.
“This is an increase and expansion of sophistication and most likely, a trial run for something to come in the future,” Rogan said.
WATCH: 2 injured in 4th recent explosion in Austin
Investigators are also concerned over the use of the tripwire.
“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, told the Associated Press.
About Austin, Texas:
Austin, with a population of nearly 1 million people, is home to the University of Texas and a plethora of tech companies and has been one of the fastest growing major U.S. cities.
Residents of the hipster city are obviously worried by the attacks.
“It’s creepy,” said resident Erin Mays, 33. “I’m not a scared person, but this feels very next-door-neighbour kind of stuff.”
*With files from the Associated Press and Reuters
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