Mayor Mitch Landrieu sought Friday to soothe the jangled nerves of his city and tens of thousands of revelers after a 19-year-old man allegedly shot and killed two men on St. Charles Avenue as the Muses parade rolled past Thursday night. It was the deadliest Carnival parade shooting in decades.

The accused shooter was arrested shortly after the incident.

Despite a robust police presence, which included video surveillance by the Department of Homeland Security, John Hicks, 19, shot Peter Dabney, 21, and Ivan Williams, 22, in the 1200 block of St. Charles between Clio and Erato streets about 10 p.m., according to the NOPD. The Coroner’s Office released Williams’ name Friday night.

At a Friday news conference, Landrieu hailed the swift apprehension of Hicks and said it showed such crimes will not go unpunished.

“If you engage in this type of behavior — if you want to wreak havoc on our city, we are going to get after you,” Landrieu said.

“We are going to find you. We are going to prosecute you, and, unfortunately, this young man is going to probably spend the rest of his life in jail.”

New Orleans Police Superintendent Michael Harrison said about 20 officers had been assigned to the immediate area where the shooting occurred.

“Our officers were on the scene and responded really quickly to this incident,” Harrison said. “Hicks and his friends had gotten into an argument with another group of individuals that turned physical and then deadly.”

The officers observed Hicks, who was wearing a black-and-white hooded sweatshirt, running from the area, Harrison said.

As he fled, Hicks allegedly threw a black handgun into some bushes at Carondelet Street and Martin Luther King Jr. Boulevard, where it was recovered by officers.

Harrison said the suspect was caught at King Boulevard and Baronne Street.

He said Hicks confessed to the two shootings early Friday, and detectives found gun residue on him, as well.

Hicks is a junior at Landry-Walker High School, according to a source close to the school.

Revelers near the shooting heard two or three gunshots, setting off a scramble, with frantic parents trying to usher their children to safety.

In remarks Thursday night at the scene, Harrison called the violence during the city’s signature celebration “extremely frustrating,” but he added that officers were “right there on the spot” and did “great work” in catching the suspect.

The parade continued to roll amid the chaos, with many bystanders apparently unaware of what had occurred. Many continued to follow floats and call for beads.

Dabney was shot in the chest and died at the scene, while Williams suffered a critical gunshot wound to the neck and was rushed to a hospital. He died about 7:45 a.m. Friday. Both victims and the alleged gunman are from the Uptown area, said Sgt. Nicholas Gernon, commander of the NOPD’s Homicide Division.

Dabney’s mother, Sarah Dabney, 56, said her son and the other victim were good friends. She didn’t think they knew Hicks.

“He was a good child,” Sarah Dabney said of her son. His death “took something from me that I can never get back.”

Peter Dabney, who graduated from McDonogh 35 Senior High School, had been working a steady job in construction on a street-repair crew, members of his family said.

When work was over Thursday, he went to his mother’s house in Central City, where he had lived until recently, and then went out to enjoy the parades.

Hicks was booked before the second man died Friday morning on counts of second-degree murder, attempted second-degree murder and the illegal carrying of a firearm on a parade route, according to court records.

His bail was set at $1 million, but with the death of the second victim, his original booking charges likely will be upgraded, and his bail could be raised as well.

The shooting wasn’t the first during a parade along the lower portion of St. Charles Avenue. In 2012, two people were shot in the same area, also on the night Muses rolled.

Landrieu tried to convey to the public — tourists and locals alike — that despite the violence, the show will go on.

“You said this was a troubled corner, and I think people are pretty discerning about that,” Landrieu said. But he added that he didn’t think it would drive people from that part of the route.

“From what I witnessed last night, after this event happened, people were still putting up ladders and getting ready for today,” he said. “So my sense is that it’s not going to deter them.”

Like the hundreds of thousands of New Orleanians who will be in the streets this weekend, Peter Dabney loved going to parades and had been going to them for years, his mother said.

She didn’t attend Muses on Thursday, and she said she had never worried about her son at these events.

“I don’t see what’s wrong with going to the parade with all that security,” she said. “He should’ve been safe.”

Staff writer Ian McNulty contributed to this report. Follow Benjamin Oreskes on Twitter, @boreskes.