MIDLAND CITY, Ala. — As FBI and police negotiators sought for days to coax an Alabama man into freeing a kindergartner held hostage in an underground bunker, the captor was planning for violence, authorities say.

He rigged the bunker with explosives, tried to reinforce it against any raid, and when SWAT agents stormed the shelter Monday to rescue the boy, Jimmy Lee Dykes engaged in a firefight that left the captor dead, the FBI and other officials said.