Police initially believed the March 2 incident was an isolated event, Manley said. "If you get a package, don't open it, man", said Julian Pina, 56, who lives about 100 yards from the spot where the bomb went off that injured the 75-year-old woman in the working-class Hispanic neighborhood of Montopolis. On Tuesday morning, Manley said that Austin police had received 150 such calls. None turned out to be a threat.
Business records indicate that Dixon was a leader of Austin's African American Cultural Heritage District, or "Six Square", which the city defines as 6 square miles of east Austin that was originally created as the Negro District by the Austin City Council in 1928.
"I don't believe in coincidences", Linder said, explaining that he was concerned by the fact that the families were acquainted. His death comes less than two weeks after Anthony Stephan House, 39, was also killed after a "device" exploded on his front porch.
Police in Austin, Texas were searching Tuesday for a bomb maker as the U.S. city remained on edge following a series of explosive packages sent to homes, killing two people.
Tina Sherrow, a retired agent for the Bureau of Alcohol, Tobacco, Firearms and Explosives, said the materials to build such bombs are commonly available at hardware stores or online, and that police have been mum on details because the perpetrators may be watching media coverage. A 40-year-old woman was also gravely injured in the bombing.
The Washington Post newspaper reported that one of the people killed was the stepson of a former pastor at a historic African-American church in Austin, while the other was the grandson of a close friend of the same pastor.
Austin Police Chief Brian Manley at first suggested that the attacks could constitute a hate crime.
Police continue to warn any residents that find a suspicious package to call 911, and to send tips to Austin Crime Stoppers at (512) 472-8477 or Texas Crime Stoppers at 1-800-252-8477.
The police department tweeted the figure Tuesday. "I want everyone in my community, if they see something that's suspicious - a package or otherwise - I want them to pick up the phone and call 911".
At the site of the March 2 bombing, there were no police, but the door to the red-brick house where the package exploded was still boarded up. Two similar packages left at separate homes Monday killed a 17-year-old and wounded two others.
Multiple sources briefed on the investigation told ABC News that the explosive devices were constructed with "enhancers", like nails, nuts, bolts and other metal pieces that were packed inside to generate shrapnel.
Three package bombs left on Austin-area doorsteps this month were constructed with a "certain level of skill", the city's police chief said Tuesday.
Police say the bombings in eastern Austin are likely linked.
All the victims were minorities, and investigators are looking into whether race was a factor.
Monday's explosions unfolded as thousands arrived to partake in the popular South by Southwest Music Festival.
"What caused this in these instances was a suspicious package that no one was suspecting or expecting", Austin Mayor Steve Adler said Tuesday.