Hours after a serial bomber blew himself up as authorities closed in, investigators discovered that the homegrown Texan who had killed two people and terrorized Austin for 19 days had left behind a list of future targets and a 25-minute “confession” on his phone, officials said Wednesday.

After hundreds of investigators swarmed Austin in recent days to stop the bomber, it was a combination of high-tech surveillance and old-fashioned shoe-leather investigating that led officials to Mark Anthony Conditt, 23, who had no criminal record.