Authorities identified the suspect as 21-year-old Euric Cain.
Peter Gold, 25, a Tulane University medical student who was shot as he was trying to to help a woman being assaulted, survived. He was in guarded condition Monday night at a hospital, New Orleans police spokesman Frank Robertson said.
The black-and-white security-camera recording shows a man wearing a hooded sweatshirt dragging a woman down the sidewalk toward a parked SUV in the 1000 block of St. Mary Street, New Orleans police detailed in a press release.
A few seconds later, a car turns the corner and parks. Gold gets out and approaches the man outside camera range.
Gold steps back into camera range with his hands up. There's no audio, but police said he was explaining that he didn't have any cash. The gunman fires once into Gold's stomach. The student falls to the sidewalk and curls into a ball.
The gunman points the weapon at Gold's head but the gun doesn't fire. He fiddles with the gun and tries two more times to shoot Gold in the face. He steps out of the camera range and a light-colored SUV drives away.
Police said the robber grabbed the woman's purse and left. She was not injured.
"His courage is an admirable example of the fact that the citizens of New Orleans are not going to turn a blind eye to crime and that we are going to fight back," New Orleans Mayor Mitch Landrieu said in a press conference on Monday, referring to Gold.
New Orleans police said Cain was arrested at his 17-year-old girlfriend's home.
Cain faces a number of charges including attempted first-degree murder, and his girlfriend has also been arrested and accused of being an accessory to the crime, police said.
"We are indebted to the New Orleans Police Department and the U.S. Marshals Service for apprehending the suspect in this case, which has deeply affected the entire Tulane community," Tulane University President Mike Fitts said in a statement.
Gold is a fourth-year medical student who did his undergraduate work at the school. His parents and sister attended Tulane as well, Fitts said.
"His story has attracted international attention, as people from around the world marvel at his bravery, compassion and strength," Fitts said.
His family issued a statement asking for privacy as they help Gold recover from the incident.
"While we deeply appreciate everyone's concern, support and prayers as our family faces this crisis, our sole focus at this time is on Peter's recovery," the statement said.
It could not be determined Monday night whether Cain was being represented by an attorney.