Gregory McMichael, 64, and his son, Travis McMichael, 34, were arrested on Thursday evening and were booked into the Glynn County Jail.
"Based on our involvement in this case...within 36 hours we secured warrants, that speaks volumes for itself to the probable cause in this case," said GBI's Director Vic Reynolds at a press conference on Friday morning.
Cellphone video showing the moment Arbery was killed has prompted national outrage since surfacing online on Tuesday afternoon, but his mother said she can't bring herself to watch it.
"I don't think I'll ever be in a mental state where I can actually watch the video. I had others that watched it that shared what they saw and that just was enough," Wanda Cooper-Jones told ABC News in an interview that aired Thursday morning on "Good Morning America."
In the 28-second video, Arbery, who is black, can be seen jogging around a neighborhood just outside the port city of Brunswick on a sunny afternoon on February 23. The footage ends with three loud gunshots.
Gregory McMichael and Travis McMichael, who are both white, told police they grabbed their guns and hopped in their truck to pursue Arbery after seeing him running in their neighborhood, because they believed he was responsible for several recent burglaries. The father claimed his son got out of the truck holding a shotgun and was attacked by Arbery, according to a police report obtained by ABC News.
The two men tussled over the firearm before Arbery was shot, as seen in the cellphone video, which was allegedly taken by a bystander.
Two prosecutors recused themselves from investigating Arbery's murder citing conflicts of interest since Gregory McMichaels is a retired Glynn County police officer and investigator with Brunswick's district attorney's office.
Tom Durden, the district attorney for the Atlantic Judicial Circuit, was assigned the case in the middle of April by the state's attorney general. Durden brought in the GBI to investigate on Tuesday evening, Reynolds said.
The McMichaels were charged with felony murder and aggregated assault charges.
Reynolds said on Friday there will be no hate crime charges. "There is no hate crime in Georgia," Reynolds said, adding, "Georgia is one of I think four or five states left in the union that doesn't have any hate crime."
The GBI is also investigating who leaked the cellphone video onto social media and threats against the Glynn County Police Department.
Arbery, who lived in Brunswick, one town over from where the McMichaels reside, was pronounced dead at the scene by the Glynn County coroner. No weapons were found on him, according to the police report.
"I'm managing, it's really hard," Arbery's mother told ABC News Thursday. "It's really been hard."
"It’s outrageous that it has taken more than two months for Ahmaud Arbery’s executioners to be arrested, but better late than never," Ben Crump, an attorney representing the family, said in a statement. "This is the first step to justice. This murderous father and son duo took the law into their own hands."
Prior to the pair's arrest, Cooper-Jones told ABC News she believed authorities hadn't taken them into custody because Gregory McMichael had a lengthy career as an investigator in the Brunswick district attorney’s office before recently retiring.
"I think that they don't feel like he was wrong because he was one of them," she said.
After the video circulated on social media Tuesday, a large crowd of protesters marched through the neighborhood where Arbery was killed. The Georgia Bureau of Investigations announced Wednesday that it was opening its own probe into the Feb. 23 incident.
S. Lee Merritt, one of the attorneys representing Arbery's family, demanded answers Thursday morning and had asked for the immediate arrests of Gregory and Travis McMichael.
"Prosecutors will need a grand jury in order to formally indict these men, but that has nothing to do with actually going out and arresting the men seen on camera murdering a 25-year-old unarmed black man," Merritt told ABC News in an interview that aired Thursday on "GMA."
"The prosecutors actually have the option, if they so chose to, to directly indictment and skip the entire grand jury process," he added. "It's something that happens all the time in our legal system, and this would certainly be an appropriate moment."
The McMichaels' attorney did not immediately respond to ABC News' request for comment Wednesday, and the McMichaels themselves did not return phone calls.
Arbery would have turned 26 years old on Friday. Cooper-Jones described her late son as humble, kind, well-mannered and beloved by his family and peers.
"Ahmaud didn't deserve to go the way that he went," she said.
ABC News' Kelly McCarthy contributed to this report.