Manley warned the public about receiving unexpected or suspicious-looking deliveries in an "average-size delivery box", but declined to offer more specifics about the packages to protect the integrity of the investigation.
The first incident occurred March 2 in a home in northern Austin.
The attacks took place as Austin hosted thousands of out-of-town visitors for its annual South by Southwest festival.
"We are having innocent people getting hurt across this community", said Austin Police Chief Brian Manley.
The packages that exploded on Monday were not delivered by any mainstream commercial shipping services, such as Federal Express or United Parcel Service, Manley said. He at first suggested that the blasts could constitute a hate crime, but later amended that to say authorities had not settled on a motive.
Authorities believe the packages were left overnight and not delivered through the mail, and were canvassing neighboring homes for any outdoor surveillance video.
The first of Monday's attacks killed a 17-year-old man and wounded a 40-year-old woman, both of them black. The explosions Monday happened at homes just a few miles apart. That incident happened at a home located in the 4800 block of Oldfort Hill Drive.
Police in Austin search for motive after string of explosions leave 2 dead, 2 seriously injured
Dixon said he did not know the third victim.
LaVonne Mason, cofounder of the Austin Area Urban League, said her grandson was the 17-year-old victim killed, but she declined to say anything further. A woman in her 80s is reportedly being treated for an "unrelated medical issue".
Authorities are not releasing any details about the devices but said they know what type of explosives were used.
Police Chief Brian Manley said Monday that investigators hope to collect surveillance video from nearby homes to identify a suspect. It's not known if the victims knew each other or if they were targeted, he said. A woman in her 80s was left with minor injuries.
An Austin teenager was killed and several others injured Monday when two packages left on doorsteps exploded, marking the second and third deadly package explosions in the Texas capital in two weeks.
In a one-on-one interview, Manley said up to 100 federal officials are helping Austin police investigate what led up to the three package explosions that claimed two lives and injured two other people. Three of the victims are black, the elderly woman is Hispanic.
The F.B.I. and Bureau of Alcohol, Tobacco and Firearms are assisting with the investigation.
With this week being spring break for grade school students, McManus advised parents to educate their children about suspicious packages and what to do if they see one. Police did not elaborate on the woman's injuries. "It's kind of one of those things that hits you from the side, especially knowing it's one of your neighbors even though you didn't know them directly", says one neighbor. Anthony Stephan House, 39, was killed by the blast, but his death was not initially ruled a homicide because it was an "isolated incident". Both explosions occurred in the early-morning hours.
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