A bitter family dispute over property in north Georgia apparently erupted Friday when a 78-year-old man threw an explosive into a law firm that represented his son, causing a blast that killed the father and injured four people in the office.

The explosion blew out windows of the two-story, colonial-style house where attorneys worked, and some in the small blue-collar town of 30,000 felt vibrations from more than a block away.

Authorities identified the bomber as Lloyd Cantrell, a man known around town for wearing bib overalls and carrying a small Chihuahua. Over the years, Cantrell amassed several parcels of land in the area, and gave some of the property to his son.

His son had grown fearful of his father, though, and filed a lawsuit seeking to keep his dad off the property the son had been given, claiming the elder man stole tools, kicked down a door and was suicidal.

Authorities said it was too early to talk about a motive in the case, but the dispute between the father and son was well-documented in court records.

"Essentially, what we've got here is not an act of terrorism," said Scott Sweetow, an agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives. "It is a depraved individual, by all accounts, who decided to launch what ended up being a suicide attack."

Police were called Friday morning to a disturbance at the firm of McCamy, Phillips, Tuggle & Fordham in Dalton, 26 miles southeast of Chattanooga, Tenn. An officer saw a man get out of a sport utility vehicle and run behind the building. The explosion followed.

Authorities think Cantrell threw the explosive through a front window or door. As of late Friday, they hadn't identified the nature of the explosive.

Inside the SUV, authorities found cylinders of natural gas, propane gas and gasoline, which they carefully removed before towing the vehicle late Friday.

Two of the injured were treated at a hospital and released, and one was admitted. A fourth, attorney Jim Phillips, was taken to a burn center in Augusta. Hospital spokeswoman Anne Cordeiro said he was in critical condition.

A block and a half from the blast site, bank executive Wayne Russell said he heard and felt the explosion.

"It sounded like a transformer that's blown," said Russell, 53, executive vice president of Omni National Bank. "We could actually feel a sort of rocking motion from the explosion."

The firm housed the office for Samuel L. Sanders, who represented Lloyd Cantrell's son in a bitter legal dispute that dated back at least two years. A police spokesman said he didn't know whether Sanders was in the office at the time of the explosion.

Lloyd Cantrell's attorney, David Blackburn, said Cantrell's son, Bruce, filed a lawsuit seeking to block his father from the land, in part claiming that his dad carried a pistol with him and threatened to kill himself.

"He has repeatedly said that 'The only thing that would keep me off the property is to be put in jail,'" according to a complaint filed by Bruce Cantrell's attorney in 2006. Several attempts to reach Bruce Cantrell Friday were unsuccessful.

The case was set to go trial in August, but it was delayed.

"I know he got frustrated because it took so long," Blackburn said of his client. He described the family as "abysmally dysfunctional."

"He was a pretty nice old man," Blackburn said of the father. "He was a little cantankerous at times, and I think he was really frustrated."

Four miles from the explosion, investigators streamed in and out of the suspect's house, which sits on a large wooded lot with a rusting tractor in front. The white house resembles a large garage with a small living area and a corrugated tin roof. A riding lawn mower and an old recreational vehicle were in the back.

Attorney Robert Smalley, a lawyer at the firm, left 15 to 20 minutes before the blast but turned back when he received phone calls about it.

"We'll take today with our families and try to regroup," he said "Our thoughts right now are with the injured and their families."

Police cordoned off the block and shut down a post office near the law firm, which specializes in personal injury and wrongful death cases, according to its Web site.

Students at an elementary school across the street were evacuated to a nearby church.

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On the Net: http://www.mccamylaw.com

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Bluestein reported from Atlanta. Associated Press writers Walter Putnam and Dorie Turner in Atlanta also contributed to this report.