A bomber is on the loose and terrorizing Austin, Texas, police said Monday, as three “related” home explosions in 10 days killed two people and wounded two others.

“We do not have a specific ideology or victimology that we have identified,” said Austin Police Chief Brian Manley, in an afternoon press conference.

In the first explosion on Monday, a 17-year-old boy was killed and his mother was seriously injured when an unexpected package arrived at their home, police said at a televised press conference. One of the victims in that case reportedly found the package outside, and opened it in their kitchen, where it detonated.

Just hours later, Austin police said they responded to another home explosion—also caused by a package—at about 11:50 a.m. The police chief, who was still on the scene of the first explosion, hopped in his car and headed to the second.

In that explosion, a 75-year-old Hispanic woman was taken to a local hospital with life-threatening injuries, Austin-Travis County EMS told the Austin American-Statesman. She is in critical, but stable, condition, said Manley.

Ten days earlier, 39-year-old Anthony Stephan House was killed on March 2 when a package exploded at his home in northeast Austin, KEYE-TV reported.

“It’s so tragic,” one of House’s neighbors told the TV station. “Everybody in the neighborhood is on pins and needles. Even seeing delivery drivers and Amazon boxes on the porch right now. Especially while we don’t know very much.”

Authorities have said they determined that the packages involved in all three of the explosions did not come through the United States Postal Service, and warned people to be careful with unexpected packages. The victims in the first two package-bomb cases were African-American, authorities said, and officials have not ruled out the possibility that the targeted attacks may have been hate crimes.

“We cannot rule out that hate crime is at the core of this but we are not saying that that is the cause,” Manley said on Monday. Police have said they are treating all three of the cases as homicides.

Gov. Greg Abbott said in a statement on Monday afternoon that he had been briefed by law enforcement.

“First and foremost, Cecilia and I offer our thoughts and prayers to the victims of these atrocious attacks,” said Abbott. “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.”

In both of the fatal cases, the packages were left on a doorstep overnight and opened early in the morning.

“I want the public to be aware and to be cautious,” Manley said. “If you receive a package not marked appropriately or from someone you know or were not expecting, give us a call.”

“This type of crime will not be tolerated in Austin,” the chief tweeted later Monday.

The Federal Bureau of Investigation and the Bureau of Alcohol, Tobacco, Firearms and Explosives are assisting local police forces with the investigation.

—with additional reporting by Julia Arciga