Local authorities in Austin said two package bombs went off within hours of each other on Monday, the first one killed a 17-year-old and the second put a 75-year-old woman in critical condition, Interim Police Chief Brian Manley said at a news conference Monday afternoon.

Why it matters: Authorities said the package bombs are probably linked to a similar incident that killed a 39-year-old man nearby earlier this month.

Other details:

• Manley said the bombs apparently went off after the victims picked up or opened the boxes.
• The motive is unknown and officials won't "rule anything out," Manley said before warning the public about accepting unexpected or suspicious deliveries in an “average-size delivery box.”
• Officials don't have a description of the suspects or suspected vehicles.
• Federal investigators including the FBI, Bureau of Alcohol, Tobacco, Firearms and Explosives, and the U.S. Postal Service are investigating the incidents.
• The AP reports that investigators are considering whether race was a factor because the victims are minorities. It also reports that the U.S. Postal Service nor private carriers such as UPS or FedEx have any record of delivering packages to the homes Monday.