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 officials said.

After the nearly weeklong hostage ordeal, relatives say the boy who turned 6 on Wednesday appears to be doing well and is back at home. He was seized off a crowded school bus Jan. 29 after authorities say the 65-year-old gunman shot the driver dead and took the child to the bunker, where he was held until Monday's rescue.

On "CBS This Morning" Wednesday, CBS News senior correspondent John Miller reported that the driver, Charles Albert Poland Jr., was what authorities described as the closest thing Dykes had to a friend.

The slain bus driver has been hailed as a hero for trying to protect all of the nearly two dozen youngsters on his bus.

Security video showed the two arguing in the bus before Dykes shot Poland and took the boy, Miller reports.

While the FBI has largely been tight-lipped about how it monitored Dykes' behavior and mood in the days leading up to the rescue, the latest revelations suggest authorities were dealing with an abductor fully prepared for more violence even as he allowed police to send food, medicine and toys into the bunker for the boy.

An FBI statement late Tuesday said Dykes had planted an explosive device in a ventilation pipe he'd told negotiators to use to communicate with him on his property in the rural Alabama community of Midland City. The suspect also placed another explosive device inside the bunker, the FBI added.

Dykes appears to have "reinforced the bunker against any attempted entry by law enforcement," FBI special agent Jason Pack said in the statement providing significant, new details about how it all ended.

CBS News correspondent Mark Strassmann reports the standoff ended when Dykes climbed an 8-foot ladder to get supplies. Sources say that, as he reached up to get a delivery, he was off-balance and vulnerable. The boy was away from the ladder and relatively protected.

When Dykes opened the door, rescue team members dropped two stun-grenades, Strassmann reports. Their loud noises and flashes disoriented him. Within seconds, four team members entered the bunker.

Dykes then "engaged in a firefight with the SWAT agents," Pack added.

Authorities believe Dykes fired first but missed, Strassmann reports. Agents returned fire multiple times, killing Dykes and rescuing the boy.

According to the FBI, bomb technicians scouring the Dykes property in southeastern Alabama found the two explosive devices.

The devices were "disrupted," Pack said, though he did not say whether that meant they were detonated or disarmed.

Officers will continue Wednesday to sweep the 100-acre property and, when they finish, investigators can more thoroughly investigate, Pack said.

For days, officers communicated with Dykes through a plastic pipe that rose up from the bunker, which was similar to a tornado shelter and apparently had running water, heat and cable television.

On Monday, authorities said, Dykes had a gun and appeared increasingly agitated, though it's unclear exactly how his behavior changed. Negotiations - the details of which have not been made public - were deteriorating. The Midland City official said law enforcement agents had been observing Dykes with some sort of camera, which is how they saw that he had a gun.

Pack declined to get into specifics, but confirmed that high-tech surveillance equipment was used during the police standoff.

Dale County Coroner Woodrow Hilboldt said Tuesday that he had not been able to confirm exactly how Dykes died because the man's body had remained in the bunker. An autopsy was to be conducted in Montgomery once the body was removed.

The boy, who has Asperger's syndrome and attention deficit hyperactivity disorder, was said to be acting like a normal kid after his rescue. And officials said there was no indication that Dykes had harmed the boy.

The boy was running around, playing with a toy dinosaur and other action figures, eating a turkey sandwich and watching "SpongeBob SquarePants," relatives and Dale County Sheriff Wally Olson said.

"We know he's OK physically, but we don't know how he is mentally," Betty Jean Ransbottom, the boy's grandmother, told The Associated Press on Tuesday. She added that she feared the ordeal would stay with the child the rest of his life.

The family was relieved and grateful for all the support in a community where ribbons, fliers and vigils all symbolized the prayers for the safe return of the boy, whom law enforcement officials have only identified by his first name, Ethan.

The boy's mother, in a statement released by authorities, expressed her thanks for all the hard work of so many officers to bring her son home. The woman declined to be identified, the statement said. During his captivity, his only comforts were a Hot Wheels car and other treats passed to him by officers.

"For the first time in almost a week, I woke up this morning to the most beautiful sight ... my sweet boy," she said. "I can't describe how incredible it is to hold him again."

In Midland City, a town of about 2,400 nestled among peanut and cotton fields, residents were relieved that the boy was safely rescued from Dykes. Neighbors had described Dykes as an unstable menace who beat a dog to death and threatened to shoot trespassers while patrolling his property armed.

Children and teachers were trying to get back to normal, though some children who were on the bus where Dykes killed the driver on Jan. 29 have not yet returned to school, said Donny Bynum, superintendent of Midland City schools. Counselors and clergy are at the school to help any distraught students.

Officials hope to eventually throw a party to celebrate the boy's sixth birthday and to honor the memory of Poland Jr. No date has been set, Bynum said.