Dozens of people rushed to help the man, including off-duty lifeguards.
"We don't have lifeguards this time of the year," surfer Richard Littauer said. "But, they were on the beach and ran down. They were amazing. They were doing CPR and did all they could to save him."
Ginger Khoury, a visitor from Albany, New York, said those making rescue attempts tried their hardest to save the man, but it wasn't enough.
"They ran as if their lives depended on it and they jumped right in and did everything," Khoury said. "There was nothing more that people could have done, it was a dire situation.”
Witnesses at the scene told officers that Medici and another man were about 30 yards off the beach when the attack occurred.
“There was a lot of blood in the water," surfer Littauer said. "Pretty bad. I saw him a couple days ago with his yellow board and his flippers. He's a really good bodyboarder, I see him in the waves, just like a surfer in the bigger waves.”
The beach has been closed for swimming, and witnesses say there was instant panic when the incident occurred.
“Many people were in the water at that point," Khoury said. "So everyone was screaming to, 'Get out, there’s a shark and someone had been bitten,' and that’s how we knew something horrible had happened.”
The deadly incident is the state's first fatal shark attack since 1936, and was the second shark attack on Cape Cod this summer.
The type of shark has not been confirmed, and several seals were seen in the area on Saturday.
The Cape and Islands District Attorney's Office, as well as Massachusetts State Police are investigating.
Update 4:22 p.m. EDT Sept. 15: Wellfleet Police Lt. Michael Hurley told the Associated Press the victim, identified only as a man in his mid-20s, died because of the injuries sustained in the incident. The man was taken to a hospital where he was pronounced dead. The beach was closed for swimming.
Original Story: Wellfleet Police confirmed the shark attack happened just after noon about 300 yards south of the beach, Boston 25 News reported.
This is a developing story. Stay with Boston 25 News for more updates as they become available.