An FBI agent walks toward the scene of one of the blasts in Austin on Monday. Sergio Flores

Updated at 5:50 p.m. ET

Within a span of several hours Monday morning, two package bombs detonated in separate areas of Austin, Texas, killing one resident and seriously injuring another and calling to mind a similar blast that killed one person less than two weeks ago. Authorities say there are marked similarities in the three explosions.

"Based on evidence that we have at this scene, as well as the other two scenes where we've had these explosions, this evidence makes us believe that these incidents are related," interim Austin Police Chief Brian Manley told reporters at the site of the third explosion.

"We are putting together a task force that will work jointly until we conclude this investigation and we arrest the person or persons responsible," Manley added. "And we will leave no stone unturned because we are not going to allow this to go on in our city."

The first blast Monday, which detonated before 7 a.m., killed a 17-year-old boy and injured a woman. Just hours later in another neighborhood, a second explosion badly injured a 75-year-old woman, who was hospitalized with potentially life-threatening injuries.

Roughly 10 days earlier another package exploded, killing 39-year-old Anthony Stephan House at his home.

There was nothing in that first explosion that "made us believe in that moment that it was part of anything larger than an isolated incident," Manley said, noting that the events Monday changed their assessment.

He noted that they do not believe the packages had been sent "by any of the official mail delivery services," saying that these "box-type deliveries" instead appeared to have been left on the victims' doorsteps overnight.

He said they are also not sure the victims themselves were the intended targets, because the packages were "left at homes where there are either multiple residents or it might even be left at the wrong address."

That said, he added, they are ruling nothing out, including the possibility "that hate crime is at the core of this." The first two packages were left at the homes of black residents, while Manley described the septuagenarian victim of the third blast as a Hispanic woman.

The FBI and agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives are helping the Austin Police Department investigate. In the meantime, Manley said, "it is appropriate for residents to be concerned."

He warned people in Austin to leave any suspicious packages untouched and call the authorities immediately.

The attacks come at a particularly sensitive time for the city, which kicks off its annual South by Southwest Music Festival on Monday. The festival — which attracts more than 2,000 artists from dozens of countries — is just one of several South by Southwest events in mid-March covering film, education, technology and gaming. More than 167,000 people attended the music festival alone last year, according to CNN.

"First and foremost, Cecilia and I offer our thoughts and prayers to the victims of these atrocious attacks," Gov. Greg Abbott said in a statement. "I want to assure all Texans, and especially those in Austin, that local, state and federal law enforcement officials are working diligently to find those responsible for these heinous crimes." His office is offering a $15,000 reward for information leading to the identification and arrest of anyone involved in the blasts. Copyright 2019 KUT 90.5. To see more, visit KUT 90.5.