Two men and one woman were killed on Saturday afternoon at a Dollar General store in Jacksonville by a white gunman carrying a weapon decorated with swastikas. The gunman, identified as 21-year-old Christopher Palmeter, shot and killed himself at the scene.
Mr DeSantis, who is running for the GOP nomination for president, has been criticised for easing gun laws in Florida and initially staying silent on the shooting. In April this year, the governor signed a bill into law that allows people to carry concealed weapons without a government permit.
As the governor began speaking at the vigil on Sunday, many members of a crowd of over a hundred people booed Mr DeSantis, forcing him to step back from the microphone.
Ju'Coby Pittman, a Jacksonville city councilperson who represents the neighbourhood where the shooting took place, stepped in and asked the crowd to listen.
"We are going to put parties aside because it ain’t about parties today," she said, adding: "A bullet don’t know a party."
Mr DeSantis shared a video on social media condemning the violence, while calling the gunman a "deranged scumbag".
"Casey DeSantis and I stand with the families impacted by the tragic shooting in Jacksonville," the governor wrote on X, previously known as Twitter. "The people of Florida stand united in condemning the horrific, racially-motivated murders."
Mr DeSantis said that on Monday the state would be announcing financial support for security at Edward Waters University, the historically Black college near where the shooting occurred, and to help the affected families.
Jacksonville Sheriff TK Waters identified those killed as Angela Michelle Carr, 52, who was shot in her car; store employee AJ Laguerre, 19, who was shot as he tried to flee; and customer Jerrald Gallion, 29, who was shot as he entered the store in a predominantly Black neighbourhood.
The gunman entered the store armed with an AR-style rifle, Glock handgun and “outfitted with a tactical vest" shortly after 1pm on Sunday.
He first went to the campus of Edward Waters University, where he refused to identify himself to a security guard and was told to leave the campus.
The gunman’s father then received a text from his son, telling him to check his computer. His parents then found “several manifestoes” written by the gunman, intended for his parents, law enforcement, and the media. The sheriff called the writing “the diary of a madman”.
The Federal Bureau of Investigation (FBI) has opened a civil rights investigation and says it will pursue the incident as a hate crime.
"Hate crimes are always and will always remain a top priority for the FBI because they are not only an attack on a victim, they're also meant to threaten and intimidate an entire community," said Sherri Onks, special agent in charge of the Jacksonville FBI office.