In an afternoon news conference, interim police Chief Dennis Eads said they were following several leads and he hoped to have news of an arrest soon.
"I'm very confident that we will find out who did this," Eads said.
The suspect is a white man, possibly Hispanic, in his late teens or early 20s, the Fort Myers Police Department said in a statement. At the time of Saturday's shooting, he was wearing a black T-shirt and a flat-billed black-and-red cap, police said.
The description was obtained through "several follow-up investigations," police said. Witnesses say the suspect used a black semiautomatic handgun before fleeing the festival westbound, toward the federal courthouse about three blocks south of the Caloosahatchee River on First Street.
Investigators have also obtained a YouTube video
and are "scrutinizing it heavily," according to the statement, which encouraged potential witnesses to send in tips and video from that night.
Police also released the names of all but one of the victims injured in the shooting: Tyree Hunter, 20, of Fort Myers; David Perez, 22 of Naples; Isaiah Knight, 18, of Fort Myers; and Kyle Roberts, 20, of Port Charlotte.
Authorities on Sunday identified the slain man as Expavious Tyrell Taylor of Okeechobee, who celebrated his 20th birthday two weeks ago, and said a sixth victim, who suffered a gunshot-related laceration, had refused medical attention.
'It cleared out fast'
According to the incident report, police had a heightened presence at the ninth annual ZombiCon gathering in downtown Fort Myers on Saturday night and were nearby when they received a call reporting that a man had been shot outside a fair-trade market near the convention.
They arrived at 11:44 p.m. and promptly found Taylor, who was pronounced dead at the scene two minutes later, the report said.
Earlier, chaos had erupted as festivalgoers fled screaming through the streets after shots rang out. It was not clear if the shooter was targeting certain people or firing randomly into the crowd, Eads said.
"It cleared out fast, and cop cars and ambulances came," said Savannah Holden, who watched the panic unfold from a hotel balcony.
The initial response was a "nightmare" for officers, Eads said, because many festivalgoers carried fake weapons as part of their costumes, making several thousand people suspects in the moments immediately after the shooting. He added that the city might need to consider whether to prohibit such activity at future conventions.
Four of the victims were taken to Lee Memorial Hospital for treatment of non-life-threatening injuries.
Detectives canvassed the area for witnesses, authorities said, asking anyone with information on what happened to call the Fort Myers police.
Organizers 'deeply saddened'
The deadly shooting took place at a festival that features bands and DJs performing for people dressed in zombie costumes. It draws upward of 20,000 attendees, police said.
Festivalgoers could enter the event through six different points in exchange for a $5 donation to Pushing Daizies
, the local artists' charity that organizes ZombiCon.
The organizers said they were "deeply saddened by the news of what happened within the footprint of our event."
"We take the safety of our patrons very seriously and take precautions in hiring security and police officers for our annual event," they said in a post on their Facebook page
. "Our prayers go out to the family members and individuals involved in the incident."
Authorities are asking for anyone with information on the shooting or who may have cell phone footage helpful to the investigation to call the Fort Myers police at 239-321-7700 or Crime Stoppers at 800-780-TIPS.