A 75-year-old woman was injured after picking up an exploding package outside her Southeast Austin, TX, home on Monday in the second blast reported in the city and the third similar incident in two weeks, Austin police said.

Interim Police Chief Brian Manley confirmed that evidence suggested that this bombing was related to two previous blasts from “box-type deliveries” that killed a teenager earlier in the day and a 39-year-old man 10 days ago.

Manley warned the public about receiving unexpected or suspicious-looking deliveries in an “average-size delivery box,” but declined to offer more specifics about the packages to protect the integrity of the investigation, the Austin American-Statesman reports.

He said the devices can be detonated by moving or by opening the boxes.

The chief said authorities did not have a description of suspects or suspected vehicles and he asked the public for help.