This week’s attacks killed a 17-year-old boy in an early Monday morning blast as he handled the package. A woman in her 40s was also caught in the explosion and hospitalized with serious injuries. Later that day, a 75-year-old woman was injured in a separate incident when she did the same. She was reported to be in critical condition with life-threatening injuries.

At a press conference Austin Police Chief Brian Manley told reporters that in each of the cases, the packages were left overnight on the victims’ doorsteps and were not mailed or sent by a delivery service. The U.S. Postal Service confirmed to investigators that the packages did not come through their facilities, according to the Austin American-Statesman.

“We do not have a specific victimology or ideology that we have identified,” said Manley. “So assigning a motive to this at this point…is not possible to do that based on the state that we’re at in the investigation.

–White man charged by police for spitting on black child at Hooters

It is not clear whether or not the victims were the intended recipients of the explosive packages, but earlier Monday, prior to the third explosion, Manley said he is not limiting the scope of the investigation.

“We don’t know what the motive behind these may be,” he said. “We do know that both of the homes that were the recipients of these packages belong to African-Americans, so we cannot rule out that hate crime is at the core of this. But we’re not saying that that’s the cause as well.”