The first bombing on March 2 killed Anthony Stephan House, a 39-year-old black man.
The bombings could be a hate crime, considering the victims are all black or Hispanic, or they could have been targeted for some other reason, considering two of the three families affected reportedly knew each other through activism in the local black community.
Authorities say 17-year-old Draylen Mason was killed Monday by an explosive left on his doorstep.
Three package bombs left on doorsteps in suburban neighbourhoods have exploded in less than two weeks in Texas' capital city, killing two people and wounding two others.
The Austin police chief acknowledged the possible link and said investigators were following up. "They brought that package inside the residence, and as they opened that package, both victims were in the kitchen, and the package exploded, causing the injuries that resulted in the young man's death and the injuries to the adult female".
Austin Police Chief Brian Manley is defending his department's statements that initially downplayed the first of three package bombs that went off in the city as an isolated incident.
A 75-year-old Hispanic woman who was wounded Monday after opening a package she found outside her home remains in life-threatening condition.
Nelson Linder is the longtime president of the NAACP chapter in Austin.
"One of the key things we're trying to understand is is there a connection between all of these victims", Manley said.
"Austin is quickly becoming a city of the privileged and the non-privileged", Dixon told the newspaper. "But we're not going to rule that out because we don't want to limit anything that we're considering".
Police say the bombings in eastern Austin are likely linked.
"Given the fact these people are people of color, that definitely gets people's attention", he said.
The Federal Bureau of Investigation and other US agencies are helping local police link the bombs to a suspect.
Austin Police Chief Brian Manley confirmed on Twitter Tuesday morning that Austinites listened to the warning.
Local police as well as the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives are working on the case.
Police said the powerful devices were similar to one another, all of them packed in parcels that were delivered at night, but not by the U.S. Postal Service or any commercial package delivery company.
"I don't look at it as terrorism, but it's terrorism of a community for sure", Sherrow said.
As the investigation continued, police received some 265 calls from anxious residents reporting suspicious packages. Authorities responded to 250-plus calls about parcels without finding any that were explosives. Gov. Greg Abbott announced a $15,000 reward for information leading to the arrest of the person or persons involved in the package blasts.
"We need to be aware because "South by" could be a target for something similar", said Trent Koch, 22, a Colorado State University student who is taking part. But he said the packages were "not at all identifiable" as a standard shipping box or standard shipping labels would be.
Jay Brewer, 52, an African-American security guard, lives a few doors down from the 17-year-old boy who was killed. The east side has historically been more heavily minority and less wealthy than Austin's west side, although that has changed as gentrification has raised home prices and rents everywhere.
The bombings in Austin occurred just as hundreds of thousands of people converged on the city for the SXSW Festival, but police have vowed to keep residents and visitors safe. But they happened far from the main events and concert venues.