Police and federal agents continue to investigate the four bomb explosions in Austin this month that killed two people and wounded four others.
At a press conference Monday, after the fourth bomb exploded injuring two men, law enforcement authorities asked the bomber to contact them and let them know what message he is trying to send, assuring him that they are "listening."
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The bombings began March 2 when a package exploded on the front porch of the home of Anthony Stephan House, 39, killing him. The second attack happened March 12 when a bomb in a package was taken into the home of Draylen Mason, 17. The package exploded, killing Mason, and injuring his mother.
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The third bomb exploded when a 75-year-old Hispanic woman picked up a package on her front porch. She was seriously injured.
On Sunday, two men were hurt when a bomb went off apparently after one of the two hit a tripwire attached to the explosive device.
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Authorities are operating under the assumption that the bombs were made by the same person.
Here is what we know about the Austin bomber’s habits:
- Prior to the explosion Sunday, the three bombs were left in packages at homes.
- Sunday's bomb was tripwire-activated.
- Sunday's bomb was in a different geographical area than the other three bombs.
- The victims of the first three bombings were African-American and Hispanic. Sunday night's victims were white.
- Fred Burton, a security and terrorism analyst at Austin-based Stratfor, told the Austin American-Statesman that he believes it is the same person doing the bombing. He may have changed bombing locations and methods to throw investigators off, Burton said.
- Common household items were used to construct the first three bombs, the American-Statesman reported.