A third explosion has been linked to two other deadly attacks at homes in Texas this month, where police are warning residents not to touch any unexpected boxes that end up on their door steps.
Austin Police Chief Brian Manley confirmed to reporters that the third blast — which followed just hours after an earlier deadly explosion Monday — is suspected of being connected to the recent explosions.
"This, again, is the third in what we believe to be related incidents that have occurred in the past 10 days," Mr Manley said. "Similar to what we have said in the earlier incidents, we want the community to be aware of what is going on."
The third blast sent a 75-year-old Hispanic woman to the hospital, while the second blast killed a 17-year-old boy and injured an adult woman who was in the room at the time of the explosion. A previous explosion on March 2 killed a 39-year-old man.
That third explosion was reported at 11.50am Monday while investigators responding to the second attack were still on scene. That second attack was reported at 6.44am on the same day after the 17-year-old boy brought a package into the kitchen from his home's front steps, detonating the device.
Mr Manley said that residents should not even touch packages that end up on their doorsteps if they are not expected, and said even picking up a package could have deadly consequences.
Officials investigating the incidents did not immediately disclose what types of explosives were used in the attacks, but said that they have not settled on any particular theories about the motivations behind the attack or who it might be. None of the packages were reportedly delivered through standard mail delivery services, Mr Manley said, suggesting that they had all been placed there in-person by the attacker.