(CNN) Witnesses say the suspects in the 1983 killing of a black man allegedly bragged about the crime for years, according to the testimony of a Georgia Bureau of Investigation agent at a probable cause hearing on Thursday.

Timothy Coggins, 23, was found stabbed to death on October 9, 1983, in Sunny Side, a town about 30 miles south of Atlanta.

Last month, Franklin Gebhardt and William Moore Sr. were arrested in the 1983 slaying, and Spalding County District Attorney Benjamin Coker told CNN they were angry that Coggins had been socializing with a white woman. Both are facing charges including felony murder, aggravated assault and concealing a death.

Thursday's probable cause hearing relied on the testimony of GBI special agent Jared Coleman, who said investigators had determined the killing was racially motivated.

Multiple witnesses told investigators they heard the suspects discuss the crime in the weeks and years afterward.

From left, Bill Moore Sr. and Frankie Gebhardt have been charged with murder in Coggins' death, while Gregory Huffman, Lamar Bunn and his mother, Sandra Bunn, have been charged with obstruction, police say.

Gebhardt and Moore allegedly indicated to those witnesses they had killed Coggins because he had been dancing with a white woman at a club on the night of October 7, 1983.

A magistrate judge ruled Thursday there was enough evidence to send the case to a grand jury, which will meet next week, according to Coker.

The 34-year-old cold case, which broke in October with the arrest of four men and a woman , was widely believed to be racially motivated, though no suspects or motive had previously been uncovered.

Gebhardt and Moore, based on interviews with witnesses, seemed to believe they were "doing the right thing" by killing Coggins, Coleman said, as if they were "protecting the white race from black people."

Witnesses tell of suspects' brags

Over the past three decades, Coleman said, the suspects, who were "best friends" and brothers-in-law, had been heard bragging about the killing at various times by different witnesses.

One witness, Christopher Vaughn, was 10 years old when he heard Gebhardt admit, a few weeks after the killing, that he and Moore had stabbed Coggins "28 to 32 times," Coleman said.

"Mr. Gebhardt stated that Coggins had been messing around with his old lady," Coleman said, referencing a girlfriend or significant other of Gebhardt's.

On another occasion years later, Coleman said, Vaughn saw Gebhardt in an argument with another man. Gebhardt allegedly told the man, "I got away with it once," Coleman said.

Another witness told investigators they were with both suspects at Moore's trailer when the two discussed the killing. They indicated they had "drug a black guy down a dirt road because the black male had been talking with a white woman," Coleman testified.

Moore, who was intoxicated, according to the witness, said he "missed the good old days when you could kill a black man for no reason."

Coleman said that just a few weeks before the two were arrested, Moore had been heard "bragging about the fact that he had been the one to stab the victim," and not Gebhardt.

Gebhardt also threatened one of his wives that, "If you keep on, you're going to wind up like that n***** in the ditch."

The suspects allegedly tried to intimidate witnesses, Coleman said. During one interview, Gebhardt told Coleman and a Spalding County deputy that if they provided Gebhardt with a list of people who were talking to investigators, he would "make them stop talking to us."

Coleman was also asked about the testimony of another witness, Willard Sanders, who indicated in interviews with investigators that Coggins' killing may have stemmed from a drug deal that went awry.

Sanders said he'd been told by Gebhardt that Moore tried to sell Coggins cocaine. Coggins tried it, but declined to buy it. Moore then "became enraged" and knocked Coggins out and stabbed him.

Larkin Lee, Gebhardt's defense attorney, told CNN the case was one of the toughest he's had to defend.

"You know about as much as I do at this point," he said. "We're going to have to piece it together, and it's going to be difficult to piece together 1983 again."

A key point of his defense will be challenging witnesses' more than 30-year-old memories, he said.

"Mr. Coker knows it. He cannot win this case," said Harry Charles, the defense attorney representing Moore. "His witnesses are the scum." When Charles was asked to elaborate, he indicated they were involved with drugs.

Gruesome details emerge

Multiple witnesses told investigators they had seen Coggins at the People's Choice Club in Griffin, Georgia, on the night of October 7. One of those witnesses saw Coggins enter a gas station across the street and meet with three white males in a gold Datsun passenger car.

Later that evening, Coleman said, another witness testified to seeing Coggins with three white males in a gold Pinto passenger car -- a vehicle that was similar in make to a gold Datsun, according to Coleman. Coggins told that witness he was going to Sunny Side, the town where his body was ultimately found.

Coleman testified Coggins had suffered numerous injuries at the time he was killed. He suffered five lacerations, 17 stab wounds and six slicing wounds, Coleman said, including several defensive injuries on his arms.

Timothy Coggins' relatives remember him as playful and always smiling.

At one point, Gebhardt and Moore allegedly tied a chain to Coggins and dragged him down the road behind a truck.

Gebhardt lived "in the immediate area" where Coggins' body was discovered in 1983, Coleman said.

Witness Vaughn said Gebhardt told him the knife used to kill Coggins was in a well on Gebhardt's property. Investigators were unable to excavate the well to find the weapon because it would have compromised the structural integrity of the house nearby, Coleman said.

Then-investigator Larry Campbell told the local newspaper at the time that there were bloodstains and tire tracks in the field where Coggins' body was found. Both his lungs had been punctured, he said.

"He had been worked over with a knife pretty well," Campbell told the Griffin Daily News. "He had defense wounds where he'd thrown up an arm and so forth."

Family remembers victim fondly

Coggins' niece, Heather, had previously told CNN that most of her uncle's friends were white, which might not have sat well with some folks in middle Georgia during the early 1980s.

She and the family remember Timothy as thin, charismatic, playful and possessing a bright smile that showcased his "beautiful, pearly white teeth," she said. Heather Coggins was 6 when her uncle died.

1983 newspaper story on #TimothyCoggins' murder offers more detail on what would become a 34-year-old cold case ... until last week. pic.twitter.com/zRAquv5zuz — Eliott C. McLaughlin (@EliottCNN) October 19, 2017

In addition to Gebhardt and Moore, two law enforcement officials -- Gregory Huffman and Lamar Bunn -- were charged with obstruction, along with Bunn's mother, Sandra.

Lamar Bunn formerly worked for the Lamar County Sheriff's Office and is now a part-time officer with the police department in Milner, about a 25-minute drive south of Sunny Side. He has been suspended without pay pending the outcome of the investigation, interim Milner Police Chief Michael Bailey said.