Two package bombs that exploded Monday at residences in Austin, Texas, killing a teenage boy and critically injuring an elderly woman, appear to be linked to a March 2 bomb that killed a man, police said at a news conference.
Here's what we know so far:
• The bombs killed a 39-year-old African-American man on March 2, killed a 17-year-old African-American male early Monday morning, and severely injured a 75-year-old Hispanic woman midday Monday. A woman also was injured in the Monday morning blast.
• The residents found the packages outside their houses, but none was delivered by the Postal Service or delivery services like UPS or FedEx, police said.
• Police also have not decided if these are hate crimes, but said that's a possibility because of the victims' races.
• "The evidence makes us believe these incidents are related," Austin Police Chief Brian Manley said.
All residents of Austin should be careful about packages, Manley said. Investigators have not come up with a motive, and he did not say if anybody has claimed responsibility. It's not known if the victims knew each other or if they were targeted, he said.
"If you've received a package that has been left on your doorstep or left in your yard or left on your driveway that you were not expecting or that was not from someone you know, then give us a call," Manley said.
Likewise, he urged the thousands of visitors in town -- many at the South by Southwest Conference and Festivals -- to be cautious. "Enjoy yourself, have a good time," he said. "But be aware, be suspicious."
SXSW began Friday in downtown Austin, bringing in thousands of people to the state capital. The explosions were not in the immediate vicinity of the festival and authorities say the bombings don't appear connected to the festival.
Authorities have identified one victim. Anthony Stephan House, 39, died from injuries in the March 2 explosion, police said. The elderly woman injured Monday afternoon suffered life-threatening injuries, Manly said.
In describing the Monday morning blast that killed the teenager, the chief said: "What we understand at this point is that early this morning is that one of the residents went out front and there was a package on the front doorstep. They brought that package inside the residence and as they opened that package, both victims were in the kitchen, and the package exploded, causing the injuries that resulted in the young man's death and the injuries to the adult female."
That woman's injuries were not life-threatening, he said.
In the second Monday explosion, the package exploded when the elderly woman picked up the package, the chief said.
The March 2 explosion was first regarded as an isolated incident. Police now classify it as a homicide.
The March 2 blast was reported about 6:55 a.m. in the 1000 block of Haverford Drive. The first Monday blast was reported at 6:44 a.m. in the 4000 block of Oldfort Drive and the second Monday blast was around noon in the 6700 block of Galindo Street.
Police were processing the scene at the first Monday explosion when the second occurred.
Manley said the packages are "average sized delivery boxes, not exceptionally large" that the residents found outside their houses.
"These are very powerful devices," he said, declining to be specific. "There's a certain level of skill required to move a device like this."
Texas Attorney General Ken Paxton urged all Texans to be cautious. "With three reported explosions in the Austin area, I want to urge all Texans to report any suspicious or unexpected packages arriving by mail to local law enforcement authorities. Call 911 immediately if you receive something suspicious," he said on Twitter.
Local police, as well as agencies including the FBI, and the Bureau of Alcohol, Tobacco, Firearms and Explosives, are working on the case.
The ATF is processing evidence from the first device at its lab and evidence from the second device will also be sent to an ATF lab for consistency.
Gov. Greg Abbott announced a $15,000 reward for information leading to the identification and arrest of the person or persons involved in the package blasts.