Two people were injured in another explosion in Texas' capital Austin, the fourth mysterious bombing in the city this month, police said today, sparking panic among the residents.
The latest blast occurred last night in a suburban neighbourhood in southwest Austin.
Authorities believe the explosion may have been triggered by a tripwire, but cautioned that they were still processing the scene.
Austin police Chief Brian Manley said today that based on the evidence that had been seen they believe a bomb did detonate.
Manley said that police were "working under the belief" that the explosion was related to the three others, but investigators still had yet to process the entire scene.
"We want to put out the message that we've been putting out and that is, not only do not touch any packages or anything that looks like a package, do not even go near it at this time," Manley said.
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Two men in their 20s suffered non-life threatening injuries in the blast.
A reward of USD 115,000 has been offered for information leading to the arrest and conviction of the person or people responsible for the mysterious blasts.
Yesterday's explosion was the fourth to rock Austin within three weeks. However, the three previous blasts occurred on the eastside of the city.
The first was a package bomb that exploded at a northeast Austin home on March 2, killing a 39-year-old man. Two more package bombs then exploded farther south on March 12, killing a 17-year-old, wounding his mother and injuring a 75-year-old woman.
Police said all three of those were likely related and involved packages that had not been mailed or delivered by private carrier but left overnight on doorsteps.
Shonda Mace, 38, lives just one block from where the explosion was reported. She was in bed watching TV when the incident first happened, she said, but soon her phone "started blowing up" with text from friends who had heard the news.
Mace told the Houston Chronicle that she has been alert since the first bombing.
"Nothing like this has ever happened before," she said. "It's just terrifying."