AUSTIN (CBSDFW.COM/AP) — A sense of fear is sweeping through the city of Austin and across Texas after three package bombs, left on doorsteps in suburban neighborhoods, have exploded in less than two weeks.

Two people have been killed in the explosions and two others seriously injured. Now police are trying to find the person/persons responsible before someone else gets hurt or killed.

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Police said the bombings in eastern Austin — two Monday and one on March 2 — are likely linked. All the victims were minorities, and while investigators are looking into whether race was a factor, they have backed off suggestions that hate crimes could be a core cause.

Here in North Texas, officials with the Dallas Police Department have issued a warning similar to their counterparts in Austin. DPD officials say if you get a package — not ordered by anyone at your home — do not touch it, do not let anyone near it and call 911. Residents are advised to do the same if a package arrives that isn’t addressed to you, has no return address or appears suspicious for any other reason.

FBI agents are going door-to-door in east Austin questioning neighbors still rattled after learning a teenager, who CBS News has identified as Draylen Mason, was killed and an elderly woman critically hurt after a packages left on their doorsteps exploded Monday.

The first of Monday’s blasts happened when a package was carried from the porch to the kitchen of a house and exploded when it was opened, killing a 17-year-old Mason and wounding a 40-year-old woman, both of them African American.

Austin police, along with FBI and Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) Agents, worked into the night collecting evidence from that home. De’Montrey McKenzie was a friend of Mason’s and says he’s still in shock. “He was going to go to college. He was going to graduate this year and they just took his life like that,” he said.

Mason, a musician who attended a local prep school, is being described as a very smart, athletic and polite young man. McKenzie said Mason had already been accepted to several universities and was making plans for the future.

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The scene near Galindo Street in Austin, Texas on March 12, 2018 where a woman in her 70s was injured in an explosion. The incident was the second reported explosion on Monday and the third in two weeks. (credit: Suzanne Cordeiro/AFP/Getty Images)

Hours after the first blast, authorities were called to the scene of another explosion also triggered by the opening of a package. That blast wounded a 75-year-old Hispanic woman, who was taken to a hospital with potentially life-threatening injuries.

In addition to Mason, police are also investigating the death of 39-year-old Anthony Stephan House, who was killed in a similar explosion on March 2.

Police said they do know what type of explosive device was used in two deadly explosions, but they are not releasing that information “to protect integrity of investigation.” But Manley described them as “not particularly large.” Officials also said that in all three cases, the packages did not appear to have gone through the U.S. Postal Service or private carriers like FEdEx or UPS, and were left on doorsteps without anyone knocking or ringing the doorbell.

The attacks unfolded as tens of thousands of visitors arrived for the busiest days of the South By Southwest music festival. The gathering didn’t appear related, but police urged tourists to be vigilant.

In a tweet, organizers of South By Southwest said they were “heartbroken by the explosions” and urged visitors to stay safe. Texas Gov. Greg Abbott offered a $15,000 reward for information leading to an arrest.

There was nothing obvious linking the three areas where the bombs exploded, other than all were east of Interstate 35 that divides the city. 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. It is also less true on the city’s northern outskirts, closer to where the first explosion occurred and where major firms like Dell, Apple and Samsung have sprawling complexes.

Monday’s first blast happened in Springdale Hills, a leafy neighborhood of houses mostly from the 1960s and 1970s. That was about 12 miles south of the home where the March 2 package bombing occurred. Monday’s second explosion, meanwhile, occurred about 5 miles south of the day’s first blast.

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(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)