Austin bombings victims families knew each other

EXCLUSIVE: Austin package bomb victim's next door neighbor reacts after blast

EXCLUSIVE: Austin package bomb victim's next door neighbor reacts after blast

The calls followed three package bombs that detonated at different residences in the city, killing two and injuring two others.

According to CBS affiliate KEYE, the explosion occurred at the 4800 block of Oldfort Hill Drive in east Austin. "Are you trying to say something to prominent African American families?"

Both House and Mason, whose mother was also seriously injured in the blast earlier this week, were black.

The bombing on Galindo Street injured a 75-year-old Hispanic woman, who authorities say remains in critical condition.

It often takes several attempts for parcel bombers to "hit their stride", and they "are rarely this effective" on the first try, a report released by Stratfor said.

The revelations toss new questions on whether the bombings were intended as random domestic terror attacks, or if they were planted with specific individuals in mind. CNN reported on Tuesday that law enforcement believe the bombs may have all come from the same maker, and that they were all "essentially pipe bombs rigged to explode upon opening".

The F.B.I. and Bureau of Alcohol, Tobacco and Firearms are assisting with the investigation. Austin police have urged residents to stay vigilant of their surroundings and report any suspicious items or behavior, leading to 150 calls to 911 between Monday and Tuesday morning; none of these calls led to the discovery of any danger.

Not many details about the construction of the bombs have been made public, but Austin Police Chief Brian Manley said "these are very powerful devices". Manley added that investigators have not yet ruled out a hate crime as a potential motive.