AUSTIN — The third package to explode in Austin this month, severely injuring a 75-year-old woman, was addressed to a different home nearby, according to people familiar with the investigation — adding a wrinkle to investigators’ efforts to identify who is responsible for leaving sophisticated bombs on the doorsteps of unsuspecting residents.

The FBI and police have not identified a suspect or motive behind the attacks, and the clues revealed publicly have only deepened the mystery. Read more.