The unidentified FBI agent who made the call to send men into the bunker said Jimmy Lee Dykes would sometimes become agitated while in the bunker and talk about his plan, ABC news reported Friday.
"At the end of the day, the responsibility is mine," the agent said. "I thought the child was going to die."
Police were careful not to anger Dykes, who shot and killed school bus driver Albert Poland Jr., 66, before kidnapping the child, identified only as Ethan, and holding him hostage for a week in an underground bunker near Midland City, Ala.
Officials believed Dykes was monitoring police reports from inside the bunker, and even thanked him at one point.
Text messages sent by hostage negotiators to Ethan's family helped them get through the ordeal, said Ethan's adult brother Camren Kirkland.
Ethan celebrated his 6th birthday Wednesday with family and friends, as well as FBI agents, SWAT team members and hostage negotiators, in attendance.