Police in Dallas have joined those in Austin and Houston warning residents to not open packages that they weren't expecting, after two package explosions Monday killed a teenager and injured two others in Austin.
Monday's detonations are the second and third package explosions in Austin this month after a man was killed March 2 by a package bomb.
Early Monday morning Austin police were called to a home in the Windsor Park neighborhood, on the 4800 block of Oldfort Hill Drive, where a package exploded, killing a 17-year-old boy and badly injuring a woman. Family friends tell NBC 5 the injured woman is the teen's mother.
"That is a good family, a religious family, will do anything for you," said longtime neighbor and friend Robbie Overton. "A cruel person would take the life of a 17-year-old, just starting out in life. I think it's cruel."
NBC 5 is not identifying the teen because police are still notifying his family. Friends say he was a senior at East Austin College Prep, a talented musician who played the bass for the Austin Youth Orchestra and had been accepted to several universities.
Hours after the Oldfort Hill Drive explosion, there was a second incident in southeast Austin where a 75-year-old Hispanic woman noticed a package on her porch, picked it up and it detonated. The blast severely injured the woman and she is currently listed in critical condition with injuries that are life threatening.
A second woman from that address has been hospitalized with an unrelated medical issue.
Police said the detonations Monday are believed to be related to an explosion at a home in the capital city on March 2 that killed 39-year-old Anthony Stephan House. That blast was originally investigated as a suspicious death but is now being viewed as a homicide.
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Austin Chief of Police Brian Manley said investigators believe the deadly attacks are related, as in both cases, the packages were left overnight on the victims' doorsteps and were not mailed or sent by a delivery service.
He said the U.S. Postal Service doesn't have a record of delivering the package to the East Austin home where Monday's explosion occurred, and that private carriers like UPS and FedEx also indicated that they had none, either.
"There are similarities that we cannot rule out that these two items are, in fact, related," Manley said.
Manley added that there is a certain level of skill required to put together a bomb successfully and that the explosions have been very powerful.
Investigators haven't determined a motive for the attacks and the chief vowed to bring them to an end, leaving no stone unturned.
Manley said Monday there is no description of the person leaving the packages and that the person is leaving the packages on the porch without ringing the doorbell.
The FBI and ATF's National Response Team are assisting the Austin Police Department in the investigations into the explosions.
NBC5's Alice Barr contributed to this report.