The standoff between police and a gunman accused of holding a kindergartner hostage in an underground bunker dragged into a fourth day on Friday, as authorities sought to continue delicate conversations with the man through a pipe and worked to safely end the tense situation.

The gunman shot a school bus driver to death Tuesday, grabbed a five-year-old boy off the bus and slipped into an underground bunker on his property in rural Alabama, police said.

There were signs the standoff could go on for some time: the shelter has electricity, food and TV, and police have delivered the boy's medication through a 10-centimetre-wide ventilation pipe leading to the bunker.

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Jimmy Lee Dykes, 65, is the suspect in a fatal shooting and hostage standoff in Midland City, Ala. (Alabama Department of Public Safety/Associated Press)

Hostage negotiators have used the pipe to talk to the gunman, identified by neighbours as Jimmy Lee Dykes, but investigators have been tightlipped about their conversations.

Former FBI hostage negotiator Clint Van Zandt said authorities at the scene shouldn't rush to resolve the standoff as long as they are confident that the boy is unharmed. He cautioned against any drastic measures, such as cutting the electricity or putting sleep gas inside the bunker because it could agitate Dykes.

'He doesn't like law enforcement or the government telling him what to do.'—Police Chief James Harrington, Pinckard, Ala.

The negotiator should try to ease Dykes's anxieties over what will happen when the standoff ends, and refer to both the boy and Dykes by their first names to humanize them.

"I want to give him a reason to come out," Van Zandt said, "and my reason is, `You didn't mean that to happen. It was unintentional. It could have happened to anyone. It was an accident. People have accidents, Jimmy Lee. It's not that big a thing. You and I can work that out."'

The shelter is about 1.2 metres underground with about 48 sq. ft. of floor space and a PVC pipe that negotiators were speaking through, said James Arrington, police chief of the neighboring town of Pinckard.

"He will have to give up sooner or later because [authorities] are not leaving," Arrington said. "It's pretty small, but he's been known to stay in there eight days."

Midland City Mayor Virgil Skipper said he has been briefed by law enforcement agents and has visited with the boy's parents.

"He's crying for his parents," he said. "They are holding up good. They are praying and asking all of us to pray with them."

Republican Representative Steve Clouse, who represents the Midland City area, said he visited the boy's mother Thursday and that she is "hanging on by a thread."

"Everybody is praying with her for the boy," he said.

Clouse said the mother told him that the boy has Asperger's syndrome, an autism-like disorder, as well as attention deficit hyperactivity disorder, or ADHD. Police have been delivering medication to him through the pipe, he added.

Command post set up at small church

The normally quiet red clay road leading to the bunker was teemed Friday with more than a dozen police cars and trucks, a fire truck, a helicopter, officers from multiple agencies and news media near Midland City, population 2,300.

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Law enforcement personnel walk away from the perimeter of the scene of a shooting and hostage taking in Midland City, Ala. A gunman boarded an Alabama school bus ferrying children home from school on Tuesday and fatally shot the driver before fleeing with a young child. (Phil Sears/Reuters)

Police vehicles have come and gone steadily for hours from the command post, a small church taken over for that use

Early Friday, activity picked up when a team in military-style uniforms, many toting weapons, got out of a big van in the pre-dawn chill and moved into a staging area. One appeared to be dog handler.

Dykes was known around the neighbourhood as a menacing figure who neighbours said once beat a dog to death with a lead pipe, threatened to shoot children for setting foot on his property and patrolled his yard at night with a flashlight and a firearm.

The chief confirmed that Dykes held anti-government views, as described by multiple neighbours: "He's against the government — starting with Obama on down."

"He doesn't like law enforcement or the government telling him what to do," he said. "He's just a loner."

No motive has been discussed by investigators, but the police chief said the FBI had evidence suggesting it could be considered a hate crime. Federal authorities have not released any details about the standoff or the investigation. The mayor said he hasn't seen anything tying together Dykes's anti-government views and the allegations against him.

Bus driver hailed as a hero

Authorities said the gunman boarded a stopped school bus filled with children on Tuesday afternoon and demanded two boys between six and eight years old. When the driver tried to block his way, the gunman shot him several times and took the five-year-old boy.

The bus driver, Charles Albert Poland Jr., 66, was hailed by locals as a hero who gave his life to protect the pupils on his bus.

The school bus remained parked on the dirt road, and trooper spokesman Kevin Cook said investigators were in it collecting evidence Friday.

Dykes had been scheduled to appear in court Wednesday to answer charges he shot at his neighbours in a dispute last month over a speed bump. Neighbour Claudia Davis said he yelled and fired shots at her, her son and her baby grandson over damage Dykes claimed their pickup truck did to a makeshift speed bump in the dirt road. No one was hurt.

The son, James Davis Jr., believes Tuesday's shooting was connected to the court date. "I believe he thought I was going to be in court and he was going to get more charges than the menacing, which he deserved, and he had a bunch of stuff to hide and that's why he did it."

Neighbors described a number of other run-ins with Dykes in the time since he moved to this small rural town near the Georgia and Florida borders, a region known for peanut farming.

A neighbour directly across the street, Brock Parrish, said Dykes usually wore overalls and glasses and his posture was hunched-over. He said Dykes usually drove a run-down "creeper" van with some of the windows covered in aluminum foil.

Parrish often saw him digging in his yard, as if he was preparing to lay down a driveway or building foundation. He lived in a small camping trailer there and patrolled his lawn at night, walking from corner to corner with a flashlight and a long gun.

Court records showed Dykes was arrested in Florida in 1995 for improper exhibition of a weapon, but the misdemeanour was dismissed. The circumstances of the arrest were not detailed in his criminal record. He was also arrested for marijuana possession in 2000.